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I know that this might not be perfect but in the US we doing multi ported number differently. If I port a a number from att to T-mobile. ATT and T mobile work it out. IfI then port the number to sprint it goes back to ATT. Then ATT and sprint work it out. The number will always be ATT. If for some reason I stop paying my sprint bill and do not port the number out, the number will go back to ATT.