Hello ..
I am trying to do this very thing. I have BB 8320 on TMO and I am trying to tether it to my laptop via Bluetooth.
I googled like crazy and followed these directions:
http://forums.crackberry.com/f3/how-use-your-blackberry-modem-19093/
I also found this on TMO site:
http://us.t-mobile.mywds.com/configurator/gt.asp?_api=GetProductDetails&ProductId=700000056068&LevelOfDetail=%2BContent&Substitute=NAME:T-Mobile%20GPRS&Substitute=gprs_apn:internet2.voicestream.com&Substitute=gprs_ppp_usernamea%20username%20is%20not%20required%20by%20T-Mobile,%20please%20leave%20this%20field%20blank)&Substitute=gprs_ppp_passworda%20password%20is%20not%20required%20by%20T-Mobile,%20please%20leave%20this%20field%20blank)&Substitute=gprs_authentication_type:%20&Substitute=gprs_pop:&Substitute=gprs_smtp:&_xsl=GetGPRSGuide&_title=T-Mobile%20Internet%20with%20your%20BlackBerry%20Curve%20and%20Windows%20Vista
But when I connect it all seem to work fine but it can not go to any web sites. Looking at ipconfig I seem to be missing network information. I have IP & Subnet but is missing default gateway. It seems that I am not hooked into a DNS server. When I go to a webpage I see it looking up the URL.
Update:
I did a diagnostic with windows and it says it can not communication to the DNS server.
Any ideas?
Thanks!