Ok so after doing a quick Google to find out a little about the company I found their own website [
Blyk].
I did my usual read on something which might save me money, including taking their "tour". Seems like they are offering you these free texts and minutes very legitimately, however by taking the free text and minutes you are then subject to up to six multimedia messages per day. Which by the looks of things you are required to reply to them, however this is free and therefore does not use up your free texts or minutes.
But you also have the opportunity to Top-Up to receive more credit for any mixture of texts and minutes you like. The only down fall to this is that you still receive the advertisements even if you have used up all the free stuff, however once again you still do not get charged.
One final word, you MUST have a colour screen mobile phone in order to receive this service. But I think that it is well worth going for as the call rates do not seem too high either.
EDIT: This is currently a UK ONLY service.