It only costs what you already pay your telephone network provider for your calls. We use 03 telephone numbers for Conicall. 

Calls to 03 numbers cost no more than a national rate call to an 01 or 02 number and count towards any inclusive minutes in the same way as 01 and 02 calls. This applies to calls from any type of line including: mobile, BT and other fixed line or payphone. International callers will need to check call costs with their network providers.