Text forces phone to connect to Internet

Elsewhere

A couple of times recently I have been sent text messages which look quite normal, yet if I hit "reply" my phone connects to the internet to do so before I can stop it - even though I haven't told it specifically to connect.

I don't have any data included in my phone package - at the moment I have no intention of using my phone for the Internet, so this irritating automatic behaviour is costing me money - only a few pence, I know, but I don't see why I should pay for something I haven't chosen to do.

Is there any way of preventing a phone from automatically connecting - or at least being alerted that a specific message is likely to trigger it? The phone is an old Motorola Razr V3.

nb. I'm with O2 - they were clueless when I rang them for help.