It is not possible to determine a cellphone's mobile network by its prefix. Phone numbers are organized by area codes. These prefixes reflect the geographical area where the phone is registered and not the specific cellphone network.
Mobile networks use the same routing and phone numbers as landline telephones, in most instances. Some large cities have a certain prefixes for landlines and different prefixes for cellular phones, but these numbers are not further categorized by cellphone carrier. The only way to determine the carrier of a particular cellular phone is to check the carrier name or ID in the mobile network settings.