Tele-Discount allows you to call mobiles through this 0871 access number: 0871 999 69 69
Calls to 0871 numbers cost 15p per minute from a Virgin Mobile phone.
I think this one works too: 0844 566 43 43 but costs the same though but from landlines its no more than 5p per minute.
www.telediscount.com
So theres the end to 35p per minute charges-saving you 20p per minute! and furthermore if you call internationally, you can even save on that too as you call many countries with the above access numbers. So if you call Austrailia from your virgin mobile you will save 25p per minute! and calling Europe with the access number, you will save 5p per minute. These rates are compared to Virgin's standard direct dialled call rates.
When dial the access numbers:
Enter the mobile number when requested you do not have to input any special codes and you do not need to put 0044 just enter the number the usual way for example this is how: 07973-xxx-xxx