Long answer: When this question gets asked, usually what the asker is looking for is a single universal number which will work with any phone of a given model, so as to lift the subsidy lock* on their phone without going to the carrier which sold it. Sorry, there is no such capability. Each phone has a unique code, and only the cellular provider which sold you the phone knows what it is.
The phone manufacturers have implemented what are known as subsidy locks. What that means is that the phones are inhibited so that a phone sold by XYZ would not work with carrier ABC, even though ABC sells exactly the same model. Usually this is done by locking the phones NAM, so that it can not be reprogrammed to use a different service provider as the home system. (This does not prevent you from roaming to the other system.)