Unlike the United States, where a specific mobile phone number can be requested, phone companies in the United Kingdom give subscribers predetermined numbers. All mobile phone numbers in the United Kingdom start with the same two digits; this way it is very easy to identify if someone is calling from a house phone or a mobile phone. On your caller ID, you will be shown the country code too.
Look for the U.K. country code, 44, on your caller ID. If the you are called from a U.K. cell phone, the number will begin with "01144" or it may be displayed as "+44."
Look for the number seven prefix. All mobile numbers in the U.K. begin with the number seven. No matter what part of the U.K. the caller is calling from, their mobile phone number will begin with the external dialling code and country code "01144" followed by the number seven.
Look for 15 total digits. This is the number of digits--including the country code and dialling number--for U.K mobile phones.
If you are in the U.K. and receiving a phone call from a U.K. mobile number, this number should begin with zero followed by seven and the rest of the phone number. If you are calling a U.K. mobile number, you'll have to dial "011447" then the rest of the phone number. Do not dial the zero directly before the seven, even if it is written down this way. The zero only applies if you're calling from within the U.K.
You cannot tell what area of the United Kingdom the phone number's coming from, since all cell phone numbers begin with the number seven, regardless of where the caller is. It is also impossible to tell what network the call is coming from.