It says it's a gift card balance equivalent to the purchase price that's automatically applied on their next purchase (+an extra £5 to sweeten the deal), so not really the same thing as the cash they originally paid for it.
You guys are being silly. Obviously that doesn't work because the speed of light limits how fast that call can come through. By the time you get the information the stock will have already moved.
Besides, the limit of bandwidth is almost entirely artificial. Yeah, it costs some amount of money to send, say, 500 SMS messages, serve 1 GB of data, or process a 5 minute phone call. But not nearly as much as you're paying and it's not like they pay per SMS/GB/minute, once the infrastructure is there they pay a fairly flat amount to keep each service area running (until it's time to upgrade but depending on where you are, that might even be publicly subsidized). So, whether you're allowed 10 GB or 20 GB per month makes barely a dent on their cost, but getting you to pay $15 for 20 instead of $10 for 10 when $20 for 20 already isn't an option is really good for their bottom line.
J'accuse!