If your present contract is with Orange, you could use your existing phone & change it to their Virgin equivelent OVP tarrif. This has no line rental, free itemised billing (necessary if you claim back call costs), free voice mail & worldwide roaming. UK calls cost 15p for first 5 mins then 5p/min for remainder of day. (No free mins).
You could get same deal from Virgin - get their SIM card to use in your own phone (assuming it is dual band as they use 1-2-1 / T mobile's network) or buy a non-subsidised phone from them.
Pay-as-you-go phones are unlikely to have itemised billing with limited & expensive roaming.