I used to work as a CSR for a cell phone company and as a general rule, if a customer went 30+ days late they MAY get reported to the credit agencies and we were told to advice the customer of this (you could call in for a payment arrangement and -to my understanding- keep the account current (also prevent suspension) with no ill effect even if you have 30+ days behind). I have seen family members get reported for 30 days and have seen others have  60 days and not get reported, it is a YMMV thing. I would expect it to report at the 30 day mark and try to avoid it.