I have good news for you: I've tried to send and receive SMS with my modem, and it work. It worked out of the box with FrontlineSMS 220.127.116.11.
For you to know, I have a Huawei E1756 provided by Digicel.
If you have any problems, there are a few trinkets that you have to do (e.g. close the Digicel client, but configure it beforehand to save locally your SMSs), you can get in touch with me or surf the forums (that's where I get the information).
It looks like you've got some great help there. I only managed to get the system running with a nokia phone while in Haiti (which I brought from the US). As Leonard said, getting Frontline to work can be problematic. However, it is isn't impossible and just takes the right combination of gadets. I wish I could help but I'm no longer in country.
Hi Jack, glad to have a fellow volunteer working here in Haiti. You're actually quite near to the central offices of my NGO (América Solidaria), who are in Delmas 56 (I live in Boudon, though).
Regarding your questions, I haven't yet started the implementation of the project, but I do have an USB modem given by Digicel. The cost is 4600 in total, 2200 is the cost of the rental, the rest is an insurance they give you back.
To get it, you only have to go to the Digicel Building who is nearby the Center Ville. You have to take a proof of residence, if I don't recall bad.
If you ever want to go for a beer, and discuss our projects, let me know!