I appreciate that you might have sourced an answer to your question elsewhere due to the delay in my response.
However, the calls included in your Talk Weekend package are; inclusive calls to UK landlines (free for the first 60 minutes), Virgin Mobile and 0870. These will be available to you at no extra cost between midnight Friday and midnight Sunday.
Unfortunately its always been a real pain getting straightforward information on any of the Virgin plans without spending several hours searching their website, going down blind alleys, dead links, unconnected info. I've never understood why they don't just lay out all the relevant information of their plans and addons in a clear easy to understand format including the extra expense incurred if you should request any changes. I've been a loyal customer of Virgin for, it must be at least twelve years but recently made some changes to my plan, I was surprised six or seven weeks later to find I had been charged a £12.00 installation/activation fee, no explanation, no reason given, they just helped themselves from my bank account, leaves a bad taste in your mouth just as finding Talk Weekend only applies to the first sixty minutes, no one told me that either.