From 4 January 2014 BT SmartTalk offer gives you 60 minutes of free calls from your mobile each month throughout 2014."Calls that normally would be chargable."

If you've already downloaded the BT SmartTalk App, make sure you've registered it by 31 January 2014. Register now on My BT.

www.bt.com/smarttalk

This is on top of it allowing you to use existing inclusive minutes. (Calls of up to 1 hour (excluding indirect access numbers and dial-up Internet access). Fair use policy applies (maximum 1,000 minutes or 150 calls a month).

See the legal bit.

" 60 minutes of free calls per month throughout 2014 for BT SmartTalk customers. Each user (up to a maximum of 5) registered against your BT SmartTalk account will get the first 60 minutes of chargeable calls they make using the BT SmartTalk service free. Unused monthly allowance cannot be carried over to the following month or transferred between users on a single account. Value of free calls for each user will be shown on the account holder's bill and total value will be applied as a discount. BT reserves the right to end the offer at any time, including before the published end date."

Dave wrote on Oct 22^nd, 2013 at 9:56am:
Yes it's VoIP.

I've found call quality ok sometimes odd bad times but only used it via wifi, not mobile internet.  Mostly when at work on lunch I use works wifi but work do have restrictions and implement QoS so that is prob reason why call quality can be bad.

BigJohn first mentioned it in this thread.