Hi guys, first time post so be gentle.
I've just Jailbroken my phone and found so many answers on here I thought I'd pass on some information I found.

I was trying to get 3G up and running and I tried pretty much everything until I saw this.

OK, here's how to do it -
Enable wi-fi on your phone.
Go here - Tutorial: How to Tether on an iPhone 3G or 3GS running OS 3.1.2 on your computers browser and save the .mobileconfig file found in step 8 (Right Click and "Save As").
Email it to yourself and open the email on your phone.
Open the attachment and install!

It worked for me. Here's hoping it works for you guys.

BTW I take no credit for this, I'm just passing the info on.