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Clearly you can set it somehow, but is is hardwired? Or changeable? What if I buy a phone from AT&T and move to Verizon, does it still talk to AT&T or now Ver

Clearly you can set it somehow, but is is hardwired? Or changeable? What if I buy a phone from AT&T and move to Verizon, does it still talk to AT&T or now Verizon? It would be an interesting security hole if one could modify the destination number and have it just send to a third party.

jfrunyon 5y ago
This is about where you bought the SIM from, not where you bought the phone from.
- yjftsjthsd-h 5y ago
  I dunno, I've seen phones with custom Android modifications per carrier; it could be both.
  - jfrunyon 5y ago
    Right, but this article is specifically talking about the SIM sending commands to the radio, not Android sending commands to the radio. Just because something could be done or is done does not make that fact relevant.
  - p_l 5y ago
    Those are handled, usually, by checking the network code reported by SIM and applying a specific package (usually on separate partition) to the system when doing factory reset. The selection of the packages or course varies, and back with smaller flash sizes it was common to have let's say only T-mobile but for multiple countries.
kmeisthax 5y ago
The SMS messages originate from the SIM - the same device that tells the baseband how to connect to the cell network. So it's not possible (ordinarily) to separate proactive SMS from the intended recipient network. However, if we designed an intentionally broken baseband that connected to two SIMs, and swapped the proactive SMS from one to be sent to the other SIM's network, it still wouldn't do much. The SMSes are sent to invalid phone numbers that only make sense to that carrier's internal routing.
kingcharles 5y ago
The AT&T SIM still talks to AT&T regardless of what network you are connected to. It has the full international number for the AT&T SMSC hardcoded into it so it can correctly route the message it is sending.
- vadfa 5y ago
  Most operators have a whitelist of SMSCs that they will let you use. Some even ignore the SMSC field and always route all SMS through their SMSC so if you misconfigure your phone you will still get to send SMS (and so you can't use an external SMSC to send SMS without paying your telco...)
  - lxgr 5y ago
    Interesting! Would that override still work when roaming internationally, though? It sounds similar to some providers implementing a "catchall" APN for data connections, which however has a habit of failing when roaming in my experience.

jfrunyon 5y ago

This is about where you bought the SIM from, not where you bought the phone from.

yjftsjthsd-h 5y ago
I dunno, I've seen phones with custom Android modifications per carrier; it could be both.
- jfrunyon 5y ago
  Right, but this article is specifically talking about the SIM sending commands to the radio, not Android sending commands to the radio. Just because something could be done or is done does not make that fact relevant.
- p_l 5y ago
  Those are handled, usually, by checking the network code reported by SIM and applying a specific package (usually on separate partition) to the system when doing factory reset. The selection of the packages or course varies, and back with smaller flash sizes it was common to have let's say only T-mobile but for multiple countries.

kmeisthax 5y ago

The SMS messages originate from the SIM - the same device that tells the baseband how to connect to the cell network. So it's not possible (ordinarily) to separate proactive SMS from the intended recipient network. However, if we designed an intentionally broken baseband that connected to two SIMs, and swapped the proactive SMS from one to be sent to the other SIM's network, it still wouldn't do much. The SMSes are sent to invalid phone numbers that only make sense to that carrier's internal routing.

kingcharles 5y ago

The AT&T SIM still talks to AT&T regardless of what network you are connected to. It has the full international number for the AT&T SMSC hardcoded into it so it can correctly route the message it is sending.

vadfa 5y ago
Most operators have a whitelist of SMSCs that they will let you use. Some even ignore the SMSC field and always route all SMS through their SMSC so if you misconfigure your phone you will still get to send SMS (and so you can't use an external SMSC to send SMS without paying your telco...)
- lxgr 5y ago
  Interesting! Would that override still work when roaming internationally, though? It sounds similar to some providers implementing a "catchall" APN for data connections, which however has a habit of failing when roaming in my experience.