Default [Q] htc inspire sim problem

Hi every one , i have been running my htc inspire 4g on the orange network here in the uk for a few years now & i want to go on the 3 network but when i put the 3 sim into the phone i get the "does not support this sim message" i bought the phone unlocked in florida a few years ago and its been a great phone. it also works fine with o2 sim & vodaphone sim but what puzzels me is that when i scan for available networks it picks up the 3 network. Just wondered whether rooting the phone would help[. thanks for any advise.