Just a thought here, because this is the problem I had and I felt like a real dummy when I realized what it was...
I have to *allow* new devices onto my network, even if they have the correct security "password" to log onto it.
I use software called
Network Magic for my home networking. When I first got this BB (April '08), I had a heck of a time getting it to connect via wifi with my router.
It would find the network, and I would punch in the security password, but connection would always fail. For the life of me, I couldn't figure it out, and was soooooo frustrated. I called T-mo BB help and they couldn't figure it out either.
Finally,
I went into my networking software and lo-and-behold, there was an "add new device" option in there. Who knew?? lol.. I'm pretty darn computer literate, so felt like such a dummy when I realized what the problem was!
My daughter (college student) got the same phone a couple months ago, and we hooked hers up to it the other day when she was home with no problem at all. Not that it matters, but *after* we got it connected to my wifi, I went ahead and upgraded her OS (thru T-mo's website) to 4.5 OS as well.
Good luck and hopefully your problem is a simple as mine was!