Pay off the device plan and cancel the airtime without further expense to yourself.
The phone is then yours and you can take a sim only deal from a network that does give you a signal.
Remember to unlock your phone for free before you leave though.
http://community.o2.co.uk/t5/Other-Products-Services/Unlocking-an-O2-phone-to-use-a-different-SIM-ca...
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