As for simple sending/receiving SMS messages, we at gtalk2voip.com use Clickatell's SMS service, which is very flexible, offers good technical support and provi

As for simple sending/receiving SMS messages, we at gtalk2voip.com use Clickatell's SMS service, which is very flexible, offers good technical support and providers a number of APIs including SMTP, SMPP and HTTP (we use SMTP). Among their cons: their rates are quite high unless you pre-pay for 1M messages a month and they don't want to provide you with a complete list of rates associated to mobile phone (DEF) prefixes, so reselling SMSes is close to impossible, cause you have no means to know how to account your own users in real time :-(. As for selling content over SMS, as far as I know there's no way for a small startup company to get into revenue sharing deals with mobile carriers, besides there are a lot many of them. Yet, there are some companies that provide paid content distribution service, which you can use to resell your mobile service, software or other content you have right for (some junk like ring-tones, pron, etc). They act as a proxy service and they take up to 70% of revenue. They usually have a small coverage of mobile carriers they work with. Also there is a very high rate of returns/chargebacks, as end-user is always right even if he completely abused your service or software :-(. We wanted to use such service to let our customers recharge their balances in our system with a single SMS sent. After I studied this subject (for Europe, have no ideas about US) we abandoned the idea as completely profitless. If you find out anything with better conditions, please let me know.