Have you installed any apps recently? That might be corrupt. The reason I ask is because I didn't have access to BIS recently and I tried all sorts of things, even contacted my provider but I eventually fixed it buy reinstalled Blackberry App World 3.0 which I had recently upgraded too. Not sure how App World has an impact on my access to the BIS server but it fixed the issue for me.
Another thing you wish to check, while it may seem obvious, is that 3G service is activated in the mobile network options. If it is just set to 2G, not sure how well BIS will work with a GPRS connection on a Torch. If I move outside of a 3G area, I also notice that the BIS symbol disappear.
Thirdly, you could try swapping out the SIM card as well with you provider and see if that has an impact.
Taking a few stabs in the dark here, but I know whats it's like to not have a working BB and I would basically try anything to get it up and running properly again.