How do I know what my cell phone carrier is?

I'm trying to upload a ringtone, but I have no clue whether my carrier is cingular blue, or orange!|||Most mobile phones have a label of the carrier when you turn on the phone. It should say Cingular (AT%26amp;T), Verizon, Sprint, T-Mobile, etc. Alternatively, check your bill. Good luck!|||call cingular?