Forum user Sbrocket has compiled a guide to jailbreaking and updating your 1.1.3 iPhone.
The guide organizes a lot of information found across the web about this potentially confusing topic:
Right now there exist, I would approximate, about 10 to 15 different guides on the web supposedly telling you how to upgrade to and jailbreak 1.1.3. The only problem with these guides is that while they for the most part contain much useful information, that information has to be pieced together like a puzzle from all the various guides. So, here you are - the definitive iPhone (and iPod Touch, soon) 1.1.3 firmware upgrade guide.
This guide will walk you through step-by-step to give you...
- A jailbroken iPhone or iPod Touch with firmware version 1.1.3,
- Working iPhone baseband radio to make phone calls, access EDGE, and use Google's new cell-tower locate feature, (ONLY if you are a valid AT&T/O2/etc customer)
- The choice to either upgrade to 1.1.3's new baseband firmware or not.