Have now paid BT £1 a month to get cheapish calls to Poland
If you pay BT £5 a month, then you can have free calls to many International destinations free for up to one hour. there is a long list on their web site. You can call anytime, as many times as you want but you have to ensure you are only on for less than an hour. You can hang up and redial again if you want to be on longer. This only applies landline to landline. It's pretty good if you call several countries on a regular basis.
Obviously, you need to be renting a BT line <goes without saying >