Originally Posted By: Arney
In Europe, I guess you could accomplish the same thing by simply swapping the SIM cards between carriers.
Yes; and you can get Pay As You Go SIMs which don't have running costs if you don't use them. (You need to use them once every six months or else risk losing the number.)

Having a spare phone is relative easy now - a matter of keeping the old phone when you upgrade. Lithium Ion batteries should keep their charge will enough that a check every 6-12 months should do.
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