I recently had the opportunity to test out an iPhone 3G, I wanted to see if I could get it to perform the same functions as my current phone - Nokia N95:

• Work with Three Ireland SIM card
• MMS/SMS/Email Messages Etc.
• Internet/Broadband/3G connection/tethering

The answer:YES, but I had to jailbreak it and unlock it in the following way.

Step 1 - Jailbreak

Using the instructions from this site I used the blackra1n application to jailbreak the iPhone, this was surprisingly easy. The reason the phone needs to be jailbroken, is so that it can install an application that allows the SIM lock to be removed (SIM Unlock). I also installed Cydia and Rock, however I don't think I needed to install both.

Step 2 - Unlock

Using the instructions from this site I used the blacksn0w application to unlock the phone. again very simple.

This allowed me to use my Three Ireland SIM card in the iPhone. The settings were automatically detected, and I was able to use the phone, internet, MMS etc. without a problem.

Step 3 - Tethering

The only niggle left, was to be able to share the phone's internet connection with my netbook, which I was able to do very easily with my N95. After a bit of searching, I found this site which carries the tethering settings for most operators, however, Three Ireland is not listed, so using their Mobile Config Generator, I inserted the settings for Three Ireland as shown below, and the iPhone installed the tethering options.

APN	Username	Password
3ireland.ie	none	none

note that 'none' above means you type in 'none', NOT leave it blank

After this, I enabled tethering on the iPhone and it showed up on my Windows 7 PC as a new network connection when plugged in via USB. However, using my Ubuntu 9.10 (UNR) Netbook (EEEPC 901) I was unable to see the iPhone when plugged into USB, however, it worked perfectly well when creating a new bluetooth pairing, and selecting the checkbox 'use mobile devices internet connection', manifested as an option (Showing BT Mac Address) when clicking on the network icon on the taskbar.

I was also able to successfully reset the phone back to the official version of the firmware.

Hope this helps! :) if you found this helpful, you can contribute £1 to me!