I have BT openzone minutes starting March 2008 for 12 months as part of my BT account. I haven't used any minutes yet and would probably only use them rarely if I keep them. Instead, I can offer my account number and password (which you can change when you first use) so that the account becomes yours.
How does £2 a month sound? Any less and it's probably worth me keeping them as I will probably end up paying for a few of sessions on internet consoles at the airports.