I always assumed I'd use some sort of baby carrier, but when I got pregnant, all I knew about were Snuggli front packs. That's what my mom had used with my sister. My midwife told me there were other things available, and introduced me to the Baby Bundler, which was my daughter's first carrier. I did not own a stroller until she was two months old, and even then, with the bus as my sole transportation, it was too unwieldy for me to use most of the time. The Bundler made shopping and nursing at the same time possible, and simplified my life dramatically.
I became more interested in baby_wearing, and was introduced to the New Native Baby Carrier when Kailea was 10 months old. It was perfect for her "up_down" phase, since I could wear it around the house with or without a baby in it. The design was simple enough that I made several slings in the same shape, but out of different fabrics, and it was a rare day that didn't have my daughter on my hip. I made some slings for friends, and for my first doula clients.
When I returned to working on a regular basis, I stopped sewing much. But still the numerous slings out there fascinated me, and I became more interested in the ways that non_western cultures found to wear their babies. It angered me that I hadn't been taught how to make a sling or carrier out of the materials at hand. It was not until I was helping a young mom with a one month old high needs baby that I started to recapture some of that knowledge. This mom was talking about postpartum, with a baby that wanted to be held constantly, and while I cleaned for her, I listened to her frustration of living on Ramen noodles during the day because it was the only food she could make with one hand. I mentioned slings, and she spoke of a dream she'd had in which she'd tied her baby to her with a sheet. She explained how it had worked in the dream, and in a flash of inspiration I said "But you wouldn't do it like that, you'd do it like THIS." I got down one of her sheets, folded it twice, wrapped it around her, tied it in a square knot, and slipped her baby into the cosy pocket the folds had made. She laughed with relief, and said, "Now I can make a peanut butter and jelly sandwich! I have two hands free!"
I was almost skipping when I left her. Here was a sling that was cheap, almost free, since everyone has bed sheets, easy to use, and easy to teach. It was a little bulky, not the prettiest sling in the world, not a long_term solution, but WONDERFUL for making life easier in the short term. No sewing was required, and the "sling" could easily become a sheet again. I still preferred my tube sling for ease of use, but what a relief to be able to provide a sling "on the spot".
I wanted to share this concept with as many midwives, doulas, and moms as possible, so that we could reclaim baby_wearing as an easy thing, not an exotic or expensive thing. At that point I didn't know much about rebozos, or different kinds of carriers and slings, just the few I'd tried. I took my idea to a Tricks of the Trade circle at Midwifery Today's Eugene '96 conference, and brought my 25 year old sheet into the middle of the circle to demonstrate this to the midwives.
Immediately Fusako Sei stepped forward and, pulling a mom and babe out of the audience, demonstrated a Japanese style of traditional carrier, using the same sheet I'd used.
Then the Inuit midwives showed us a variation of that carrier, and at that point the mom asked me if she could have my sheet, it was so comfortable.
Then one of the Mexican midwives brought out her rebozo, and showed us a variety of carries, some similar to the one I'd done, and others very different.
It was a cascade of shared knowledge that quenched my thirst for this fundamental information. I've since read a precious book called "A Ride on Mother's Back", which is a children's book about slings around the world. It's beautiful, and shows how very many ways there are of wearing a babe.
I feel very strongly that every mother should know how to wear her baby, whether or not she chooses to use that knowledge. How many times have you seen a mother juggling a stroller, baby, diaper bag and a toddler at a bus stop? How many times have you seen a parent with weary arms lugging a 30 pound toddler through a mall, carrying the child because little legs got tired?
We as birth professionals should know these techniques, and pass them on to our clients. We are in a unique position to influence our clients, and this particular influence can have far_reaching effects on the quality of life both for the families we serve and for their babies. We need to reclaim the wisdom of carrying our babies, and share it with our clients and our children.

IDEAS:

1. Make tube_slings out of birdseye fabric (cheap, sturdy, cotton diaper fabric, not flannel). Donate them to your local NICU or labor and delivery ward. Cost: $3_$6 per sling. Time: 10_30 minutes per sling

2. Buy bed sheets at Goodwill, the Salvation Army, or other thrift stores. Cut them in half, serge or hem the raw edges, wash them, and then use them as slings you can give away if you see tired moms in the mall or grocery store hip carrying a toddler or baby. Give them your business card at the same time. Cost: about 35_50 cents (yes, cents) per sling. Time: 5_30 minutes per sling. (Overlock sewing machines make this ludicrously easy.)

3. Make your clients tube_style slings out of cotton interlock as a birth gift. Or add the cost of fabric onto your fee if they want a sling. Cost: $4_15 per sling. Time: 30_40 minutes per sling, including fitting. If you want to get fancy, get or make labels with your name, practice name, and phone number on them, and sew them onto each sling. This is great advertising, both for baby wearing, and for midwifery/doula services.

4. If you don't sew, or don't have time for sewing, have your apprentice do it, or see if you can find a sewing circle or church group which would like to donate their skills to making slings for low income moms. The "bed sheet" style slings using recycled sheets is a wonderfully easy way of making "giveaway" slings.

Techniques:
Bed sheets:

Take any flat sheet larger than a crib sheet and smaller than a king sized sheet.
Fold it lengthwise, and then fold it lengthwise again. At this point you will have a long strip of fabric.

Find the middle of the length. Place the thickest fold "down" on the hip of the person who will wear the sling.

Bring one end of the folded sheet up behind the person's back and over the person's opposite shoulder. Bring the other end up in front them, across their body and tie the two ends of the fabric in front of the shoulder, so that the knot is in front of the shoulder, and the fabric is spread out a bit across the shoulder and across the back. Don't tie the sling too tightly_leave a bit of "play," which can be snugged up after the baby is in the sling. This creates a "pocket" of the sheet, into which the baby will be put. Hold the baby on one shoulder, with one hand. With the other hand, pull apart two of the layers of the sling, and guide the baby's feet in between.
Holding the sling open, use the other hand to allow the baby to slide down slowly into the sling "pocket."

Newborns will snuggle into a ball between mother's breasts. They can be adjusted a bit so that the knot or the fabric helps to support the head. A rolled up washcloth works well to support the head. Older babies will go more "off center," toward the hip, and may want to be looking out more. They can sit in the sling facing mom or facing out. Once baby is in place, the knot can be loosened slightly, then the sling can be snugged so that the baby stays easily in place and mom feels secure. Once a good fit is achieved, it is unnecessary in most cases to repeatedly tie and untie the sling, as it can be simply slipped off over the head and slipped back on the same way.

If the fabric slips, it can be safety pinned with diaper pins or sewn in place once a good fit is achieved. I find that once the sling is tightened, it doesn't slip if a square knot is used.

If desired, for a lighter weight sling, a twin or queen sheet may be cut in half lengthwise and hemmed down the cut edge. This will only need to be folded once. It makes two slings, and is a good thing to do with sheets from a second hand store. These make great hip carriers.

To make a hip carrier out of a length of fabric, simply tie it in a sash, with the knot in front of the shoulder, and sit the baby on the bottom of the sash on the hip.

A long strip of fabric can be turned into a back carrier by placing the middle of the fabric behind the child's back and bringing the fabric under the child's arms. The child is then placed high on the parent's back, with the parent leaning forward a bit. (There's a knack to this which involves keeping a hold on the fabric while swinging the child around to the back, then using the fabric to hold the child in place while the "sling" is finished). The ends of the fabric come over the parent's shoulders, cross in front across the parent's chest, and then wrap around behind the parent, over the child's legs, and then tie under the child's bottom in the middle of the parent's back. This allows the child's and the parent's arms to be free while securely keeping the child on the parent's back. This is a comfortable carrier, and does not displace the parent's center of gravity to the same degree as a backpack does. It also distributes the child's weight in such a way that the parent does not have to "hunch" over to keep the child in place the same way they would with a "piggy_back ride." It's a comfy way to carry a walking child who is a bit too heavy for a sling. The same theory can be used to make a warmer back_carry that's good for both toddlers and babies as young as about 3 months. Instead of a long strip of fabric, a very large triangle is used, and the child's arms may either be free or trapped by the fabric.
The knot secures the "point" of the triangle, making a large shawl for the baby and mother. The general placement and technique are similar. The baby rides fairly high up while the carrier is being tied, then slips down a little once the knot is in place.

A rebozo (a very large woven scarf) can be slung over one shoulder and tied at the opposite hip to tie a baby on, similar to the bed sheet sling. Or it can be folded and tied in front of the shoulder. There are a number of other possible carries with it, but I am not sure how they are all accomplished.

http://www.ida.net/users/stace/sling.html has some good instructions and pictures of how to make a tube sling.