What exactly is cell phone “roaming” and when should it work?

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I live in a moderate size city with overlapping coverage from many cellular providers. I’m not sure what the problem is today, but Verizon service has been down for about 6 hours across the city. All the phones of Verizon users are in SOS mode.

Why are we all not “roaming”? I guess I’ve always thought you enter roaming when you can’t reach a tower from your own provider, but I am in range of several other providers. My 12yo’s emergency cheap phone on Tello/T-mobile is connecting just fine. Is roaming geographically locked instead of accessibility locked? (ie T-mobile knows a Verizon cellphone at my address should be able to hit a Verizon tower so they don’t care/can’t see that I cannot currently make calls).

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2 Answers

Anonymous 0 Comments

Roaming requires an agreement between the phone company that the SIM/phone account is part of, and the phone company that owns the tower the phone can connect to.

This is typically only done for international connectivity or sometimes for connectivity in which a phone company has no presence at all (as in they don’t have any towers in a certain state for whatever reason).

The agreement is both financial (how much the first company will pay for users roaming on the other’s network) and technical (the companies have to have some sort of interconnection at some point so that the account can be verified as valid).

There are rarely, if ever, roaming agreements between carriers that both have actual coverage in an area, other than mandated exceptions like 911.

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