Some of the answers to FAQs post the jailbreak on the 3G iPhone is as follows (again I picked this from Mr. iPhone Fan's Q & A with his bloggers)
- Is there a need for Activation (SIM card) after jailbreak? No
- Does the data privileges provided by the Service Provider during purchase (factory defaults) work after jailbreak? Yes
- What happens to Warranty after jailbreak? Common sense, you think Apple will entertain your iPhone?, you can always Restore settings to Factory mode via iTunes
- Can you continue to "upgrade" iPhone firmware every time Apple releases a new update? Yes, but No Gurantees.
- What about all the data on the iPhone before jailbreak? Always Backup via iTunes and then choose the Restore option after jailbreak. Please note, data backup is limited to Contacts, Messages, Mails, SMSs and you will loose all customization (themes, ringtones, wallpapers). You can now also Backup your Media in iTunes 7, click here
Get going and "pimp" your 3G now!!
Disclaimer: "If the instructions on my page work for you, I know you and if they dont, I dont know you"