Rings before voicemail kicks in

[#1]

Is there a way to make the phone ring for longer before voicemail is activated? We have two phones in the house - both downstairs. When we are upstairs we don't have enough time to get to the phone before voicemail activates. If we could add, say five more rings that would probably do it.
Thanks.

[#2]

How long does it ring at the moment? It used to be 7 rings before it kicked in.

[#3]

If you have Call Minder you can increase the rings to 10 which is 30 seconds.

[#4]

There is a lengthy (year-old) thread on the topic here.
http://community.plus.net/forum/index.php/topic,61725.0.html