What Z/OS?
I also have a T610 with T-mobile. It works great with my c860 Cacko 1.21b and Blue Monkey CF card.
Under c860/Cacko just select Dial-up (Bluetooth), and put in *99***2# as the phone number, under modem tab search for your phone BT MAC.
You may need to create CID 2 on your phone with an APN of internet2.voicestream.com (for North America).
Alternatively you may want to create another CID to use internet3.voicestream.com. You will have to call T-mobile first if you want to use internet3. internet2 is behind a firewall and uses NAT. internet3 puts your Z directly on the net. Make sure your secure any services (e.g. ssh).
Benchmarking internet2 vs internet3 returned the same performance. I find that if I ssh with compression to my ISP and port forward their proxy to my Z and setup Firefox to use it that I get ok performance.
Any know of a good web accelerator solution for Linux I can port to the Z?