I have just found a roaming sim card at
Free Roaming SIM, Cheap Roaming SIM - Free2RoamSIM recently. Digging a little further I also found some other websites which are relatively identical:
Cheap call rates for making and receiving calls while abroad - SIM4Roaming
Cheap call rates for making and receiving calls while abroad - Travelfone
Cheap call rates for making and receiving calls while abroad - Sim2Roam
Cheap call rates for making and receiving calls while abroad - Sim2Go
Their rates are quite reasonable with free incoming call in many key countries. The sim card comes with an UK number and there is no monthly charge and connection fee whatsoever. Moreover the calling credit will never expire.
Sounds good but I don't know I can trust them or not. Have anyone tried these sim cards yet?