By default there are several things missing on the iPhone 3g such as video recording, tethering, skype, voice alerts, the ability to sync over wifi and more.
Apple runs a tight ship, and only allows installing third party apps and syncing music via iTunes. Unfortunately iTunes is only available on Windows and OSX 4 or higher (for iTunes8). Apple has also received a lot of critisism for not being very open regarding their approval process and only approved Apple approved apps make it to the App store.

This is the best and easiest to follow method for jailbreaking the iPhone 3g on Windows.
Disclaimer: Jailbreaking your iPhone could void your waranty.
I am in no way responsible to any damage that may result by following this tutorial, so proceed at your own risk!

This method works really well and does not require any patches to get iTunes working.

Before you start, make sure you are running iTunes 8 and make sure your iPhone is running version 2.1
To see what version your iPhone is running goto Settings / General / About on your iPhone.

MyMote is an awesome MythTV remote for the iPhone.

The best part about it is that the progam guide displays on the remote allowing you to quickly scroll through the program guide with the iPhone finger flick scrolling thing.
Before I got my iPhone I was using my N800 or a standard remote via LIRC as my MythTV remote, but MyMote is much better.

MyMote is available as a free install from the app store. So you don't even need to jailbreak the iPhone to get it .
Just search for "mymote" and install.

I recently called AT&T support for help setting up my new iPhone 3G.
The AT&T menu system wouldn't recognize numbers entered via my iPhone dialer.
Initially the menu recited my mobile number and asked me to press 1 to verify it was correct. I pressed one and was then asked to enter my mobile number. After entering my mobile number I was asked to enter it again in an endless loop.

I just got a new I-Phone a couple of days ago, so I haven't had a chance to play with it to much.

I have an older G3 Mac running OSX 10.3, but primarily run Linux. I also have a desktop running Windows XP, but primarily use that as a dumb client and login to my Linux systems via NX from http://www.nomachine.com.