It is already written in decimal form.
0121 serves the Birmingham, England area for telephone networks.
The area code 0121 is in Birmingham.
In the UK, 0121 is the area code for Birmingham.
Assuming that is a UK phone number - 0121 is the area code for the City of Birmingham.
0121.........
0121 do 1
0121 do one
0121 - indicates a number from Birningham, England.
646-555-0121
The answer is 555-0121
0121 is Birmingham