I recently joined the Three 321 pay-as-you-go network.
I attempted to tether my tablet to my phone just yesterday not realising that it's supposedly not possible under pay as you go. (I used my phone as a wifi hotspot.)
It actually worked pretty well, although I occasionally had server errors when connecting to paypal.
Curiously a chunk was taken out of my credit even though they gave me over 100MB worth free data due to my last top up. I thought maybe I had used up the free data, (although I couldn't see why that much so quickly) but on checking later, it hadn't gone down much at all. It seems it circumvents the free allowance when you tether.
So I checked on Three how much they charge for tethering and it was then I found out that I couldn't do what I had done.
Edited by deleted (Sat 17-Aug-13 22:48:14)