I have finally gotten my N800 to tether with my T-Mobile Blackberry Curve (8320) using the blackberry internet add-on with software version 4.2.2.180.

Setting up the connection

1. Pair the phone with the N800, making it a trusted device
2. Create a new connection with these options
Connection type: GPRS
Access point name: wap.voicestream.com
Dial-up number: *99#
User name: user (doesn't matter)
Password: user (doesn't matter)
click Next
3. Go to Advanced > Other
4. Add the Supplementary AT command: AT+cgdcont=1,"IP","wap.voicestream.com"
5. Click OK

Connecting to the internet

**NOTE** You MUST do a soft reset on the blackberry before you tether EVERY time.

To do a soft reset, press the ALT, RIGHT SHIFT, and DEL keys together

Even if you connect successfully, if you attempt to connect again later, do a soft reset on your blackberry first. I consistently connected when resetting the blackberry before attempting to tether.

I also was able to tether on my Ubuntu 7.10 system through bluetooth, so if anyone would like the options and instructions I can post that too.

I hope this helps someone out.

B