3G 8GB, OS 3.01 w/ MMS & Tethering
Here's the order of how I did things:
1. Installed OS 3.01
2. Jailbreak (not required)
3. Enabled tethering via help.BenM.at
4. Installed Carrier 5.0 (didn't input any settings, as it just worked after reboot)
= both MMS & Tethering