> developing a small mobile application and am unsure which technology to use. Initially, it will be very simple updating a few fields in an invoice table with MSSQL as the backend. Blackberry, Windows Mobile, Web App ? I would like to use the MM framework with the web service connection as the backend.

We've done / are doing this. We're using the MM Framework for the web service back end, it works great. The MM Business classes are shared with other back-end processes (eg HTML web interface)

On the PDA we're using Windows Mobile because that allows C# development on both client and server. Also, using Windows mobile the handwriting recognition is very good and we get it for free in our app (any text box is handwriting enabled). This is important for our user base would would resist learning any special techniques for PDAs - if it got too difficult they'd go back to their clipboards.

However we're not using the MM classes there, just raw windows forms, mainly to keep the size down. The PDA app is pretty simple, and doesn't need any kind of database or security framework: any local data is stored in XML files (and even XML is a kind of overkill). I haven't even checked out the MM Winforms classes for Compact Framework compatibility. I suspect quite a bit of customization would be required. Certainly in .NET CF 1.0 there were whole swags missing (eg System.Configuration) although .NET CF 2.0 is a whole lot better.


As far as the web service goes, at the moment I've gone with a SOAP-style because that's a doddle to create with the Windows / MM tools, but you could do REST-style without much effort too, you'd just have to implement the web mechanism yourself. Search for REST + ASP.NET on the Internet and you'll see lots and lots about this. I'm considering switching to REST when the API needs to be made public.

> The application will eventually become more complex adding credit card payments etc... I would like to support more than one device. Any suggestions on which technologies to use will be appreciated.

Handle the credit card payments on the back-end. Consider using a web browser on the PDA and implementing all the UI in HTML - just skin it carefully for the limitations of the PDA. Unless of course you need it to process payments off-line.

Supporting more than one device - well there isn't really any universal platform, except perhaps Java. .NET compact framework is supported on Windows Mobile / Pocket PC platforms and that's pretty much it, although there are some linux-based PDAs that gain support through Mono (not exactly big market share here). Web browser is the most universal but doesn't work offline very well.