Version 1.1.3 of the IPhone software (latest version) is currently not jailbreakable which means you cannot install any third party apps.

I have just upgraded my Iphone, it was a difficult decision as was a weigh up between keeping my 30 something apps on the phone or losing it all to the new features such as faux GPS (see feature set here).

I decided to upgrade. There is no problem upgrading a jailbreaked phone, the only downer is that you lose all of the third party apps. You don’t lose your contacts, email or sms. Do not fear! Upgrade now it’s worth it!

On a side note, mid-febuary will see the release of the iphone sdk so loads good stuff to come!