If I may be a bit provocative: why spend all that energy and time if you're not sure you can make money with it?
We did a group chat product at groupflier.com and got great traction on the free version but the SMS costs killed us and we had to switch to a paid model. Happy to trade PM on our experiences if you are interested and have a blog about it at:
http://gcrawshaw.posterous.com/group-texting-is-a-telco-game
@stangeek - can you not at least test part of your business model at the current level of traffic? Really worth getting those uncertainties out of the way... if only so you can start pivoting towards something workable right away instead of waiting a few more months.