look on cydia and look for the update info on there. i read something today from the folks that do ultrasn0w. I believe they have it in beta for ios 5 if i remember/read correctly.
Yes I have 1.59.00 BB ip4 with iOS 5. I used Sn0wbreeze v2.8b8 to jailbreak/preserve baseband and ultrasn0w 1.2.4 to unlock. Currently running Tmo, no problems with working MMS, no FaceTime.
Just remember it is a tethered JB, this is my first time not using an untethered, not a big deal since I hardly ever restart my phone anyway.