BT SmartTalk is just an app isn't it?
All it does is allow you to make phone calls via the internet on your smartphone, which are part of your BT call package. i.e. if you have free evening and weekend calls to local (or other) numbers or whatever your deal is with them, the same calls are free using the app. I believe it also gives you a separate incoming number to use with the smartphone. It's handy if your overseas and have WiFi then you can make calls to the UK free/cheaply.
There is no SmartTalk hotspot as such, any WiFi will do. All the BT hotspots (e.g. BT OpenZone) and the ones shared by other users such BT Fon/BT WiFi etc should all be free to you. Just need to sign in with your BT ID.
I guess it's not a lot of use without a Smartphone, but may work on your tablet.