Mobile phone numbers
07821 numbers are for mobile phones in the United Kingdom.
All UK 07 numbers are for mobiles, pagers and personal numbering.
Which network is 07821?
07821 numbers are allocated to O2.
Although these numbers are issued to this operator, customers are free to take their number with them when they change networks. The 07821 prefix is not a reliable indicator of which network a phone is currently connected to, only which network issued it originally.
Formatting an 07821 number
There is no set format for UK mobile phone numbers, but the commonest format is: 07821 xxxxxx
For international callers, use: +44 7821 xxxxxx