While I agree that Twitter Bootstrap != jQuery Mobile, you can develop mobile sites with Bootstrap. After spending the last couple months developing a mobile site using jQuery Mobile, my conclusion is this:
The concept behind jQuery Mobile is perfect. The "page" concept integrates very well with server side technologies (ASP.Net MVC in my case). It allows you to develop pages as individual files, rendered mostly on the server, as you're already used to doing and probably desire to do.
However, in its current state, it can get very slow and very buggy if you try to do too much with it. I've run into problem after problem with it on my project.
So I'd say, if your site isn't too complicated (e.g. no swiping, no wizards), then go with jQuery Mobile. Otherwise, think about waiting for the project to mature. It's almost there.