Because that's how things are, at least in some locations. When you move to another city or state, you either suffer extra roaming costs (and incur some on your

Because that's how things are, at least in some locations. When you move to another city or state, you either suffer extra roaming costs (and incur some on your peers, as they'll be calling "long-distance" numbers even if you're physically close), or get a new (local) SIM/phone number. At least, that's what my experience is. This must be even more true when moving to another country. (Surely, there also must be some exceptions as well, where maintaining old number is an option.)