Can i unlock my japanese iphone in the uk?

28-12-14

i live in the uk

i got a gift from my unkle who lives in japan. he gave me a iphone 5. i updated the software and the phone went to the activation screen. the phone is asking me for a sim but when i put in my uk sim it says 'sim not valid: the sim card that you currently have installed in the iPhone is from a carrier that is not supported under the activation policy that is currently assigned by the activation server... please insert another sim from a supported carrier or request that this iPhone be unlocked by your carrier'...

01-03-15

So i asked my unkle to send me the sim and he did. (its a softbank phone) . I inserted it and it activated. so now my only issue is that i cant use it with a uk sim because it is still a locked phone. so i need to know if there is any way i can unlock the iphone so that it is usable with a uk sim.

is there?? if yes, then what is the price of this??