7726 is spam using the number keys. Makes it easier to remember :-) The 8 that Vodafone uses is a V, so that's easy too - as is the 3 that 3 uses.
Recently needing to do this, I came across this very helpful table courtesy of Money Saving Expert.
If you receive a spam text message, all you need do is forward it to the relevant number, making for a wonderfully simple and quick way of reporting it and so doing your bit to help tackle text messaging spam:
| Network | What to do? |
|---|---|
| O2 | Forward message to 7726 |
| Vodafone | Forward message to 87726 |
| Orange | Forward message to 7726 |
| T-Mobile | Forward message to 7726 |
| Three | Forward message to 37726 |
