[Mr_Moo]

Alternatively you could have the amount of seconds changed on the switch (exchange) by calling customers services as a 'change request', therefore letting the phone ring longer.

3 seconds = 1 ring.

And you could have 'message waiting tone' so all you would need to do is lift the handset when you got home and if the dial tone was stuttered, then you have a message waiting. No messing around with 1571...