We have 5 networks in UK ,Vodafone , o2 , Orange , Virgin and T-Mobile . the phones work on Orange and Virgin , I havn`t tried T-Mobile.
I think they are blocked by Vodaphone :-( I have tried Pay as you go sim cards from both Voda and O2 and none of them work . I think they have been blocked at the network end , maybe like they block stolen phones? but Im no expert on this!
TomH