@Malenfant said:
Actually, I believe this is a legacy from the way BT was originally privatized. They are a telephone company and there is a requirement to maintain this as their primary function even when selling other services. BT are not allowed to sell you broadband without you having a BT line, whereas other ISPs can. I don't know the exact details, and can't be bothered to look them up, but I imagine there is a regulation that stipulates a minimum amount of calls in order to keep the pretence that this is primarily a telephonic contract.
It's nothing to do with privatization; BT want you to use the line as your preferred option for making calls, rather than having you always reach for your mobile. The hope is that you'll either pay extra for a calls package to avoid being charged for the calls (money for BT beyond line rental), or accidentally make a call not covered by your allowance (e.g. calling during peak times when your allowance only covers off-peak).
By insisting that you make two calls a month from your BT line, BT hope to ensure that you've always got the landline available, and are prepared to consider it for every call you make. If you've not plugged in a phone, or have put the phone somewhere unreachable, they get to charge you a pure-profit £1.50/month, more than compensating them for the missed revenue from the calls you might make.