Fring is a cool service, Fring on the iPhone is below zero kelvin! I just installed it -thanks to mikew41- and Fring is ral real cool. To give you an idea on what it can do

1. import jabber / gtalk friends and chat with them via Jabber
2. import friends from other Instant Messaging service and use the service. I do not use these but think MSN, Y!, ICQ etc
3. setup your twitter account and have a multitasking twitter client in the background (keyword: background)
4. Import Skype contact, sign in and USE skype over Wifi!
5. Setup SIP and use your iPhone to make real VOIP calls over wifi over the internet

As you can see, a switch army knife. Skype by itself would have been cool enough for me, SIP a great much needed add on. But this is an application that communicates with all services I use and acts as the information hub between my twitter, my XS4ALL VOIP, my Skype and my jabber friends. I think it it the best application available on the iPhone. Installation is a 10 seconds job once you are in "installer" (you do have a jailbroken phone I hope?). Simpley ad the repository to installer, tab on fring and you are ready! This is great.