The service is very simple, here's how it works:

Stage 1
Register as a customer following the step by step instructions. All we need is your name and email.
Stage 2
We give you UK numbers to dial instead of your existing UK mobile or international numbers. Dial the new UK number the service has given you beginning with 08 or 09.
Stage 3
The service connects your call, terminating to the original international or UK mobile number.
Stage 4
You can talk to your friends and family for as long as you like without worrying about the cost.