Here's the link to the form where you can choose "suggestion" and write one in the space provided:
AOL Click here
Here is the message that I sent to Yahoo, just in case you were curious:
I'm writing in with a suggestion for you when it comes to Yahoo! Messenger Avatars. I applaud you for making all skin tones and all hair types/styles available to everyone to choose for their avatar, but you're missing a large part of the picture, literally! All of your avatars are of thin women and they all look like they weigh 100 lbs. There isn't a single face, shirt, pants or anything catered to big women. If you're trying to make it a diverse selection, perhaps adding stuff for big women (and I don't mean "size 12" big women) would really be a nice advantage for me and people like myself. Many of my friends (including myself) are 300 lbs.+ and we'd also like for our avatars to resemble what we look like, too! Give us a chance, Yahoo! Thanks for hearing me out!
If you've decided to take a stand, comment and post your letter!