So managed to Jailbreak my iPhone using redsn0w, installed Cydia and installed ultrasn0w 1.2.5 for the carrier unlock. However, when i start the phone i get either "No service..." or "Searching" where my service bars should be.
Attempted to restore 5.0.1 FW via. iTunes, jailbreak and re-flash the Baseband with redsn0w to no avail.

iPhone 3GS
New Bootrom
iOS 5.0.1
Baseband 06.15.00
redsn0w 0.9.10b5c

Any ideas/help greatly appreciated! =]

you need to unlock it after jailbreaking your phone. it is not just installing ultrasnow. you need to unlock it. you can unlock it using ultrasnow procedure or you can use some other methods like remote unlocking service to get your phone unlocked. for this service you can contact Prounlocking.com