Your cellular phone will probably do a check-in with the network
every 30 minutes or so.
I base this on the regularity of my phone checking in to the
network when I have it near a radio and get a little interference
on the radio from the phone transmitting.
The network can probably control this by sending out a roll call
request.
Your phone also sends an identification when you turn it on.
... Documentation - The worst part of programming.
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