You can accomplish this by using the COR list, if you have not worked with cor-lists before then you would need to understand it first otherwise you will end up troubleshooting it for hours.

Example:

You will need to play with Inbound/Outbound assignment of cor lists: In this example here Phone 1 will use the dial-peer 100, phone 2 will use dial-peer 200 and phone 3 can use all of them.

dial-peer cor custom
name pt-portone
name pt-porttwo

name pt-portthree

dial-peer cor list css-portone
member pt-portone

dial-peer cor list css-porttwo
member pt-porttwo

dial-peer cor list css-portthree

member pt-portthree

dial-peer cor list css-phoneone
member pt-portone

dial-peer cor list css-phonetwo
member pt-porttwo

dial-peer cor list css-phonethree

member pt-portone

member pt-porttwo

member pt-portthree

dial-peer voice 100 pots
destination-pattern 9[2-9]..[2-9]......
corlist outgoing css-portone
port 0/0/1:23

dial-peer voice 200 pots
destination-pattern 9[2-9]..[2-9]......

corlist outgoing css-porttwo
port 0/0/2:23

dial-peer voice 300 pots
destination-pattern 9[2-9]..[2-9]......

corlist outgoing css-portthree
port 0/0/3:23

ephone-dn 1 dual-line
cor incoming css-phoneone

ephone-dn 2 dual-line
cor incoming css-phonetwo

ephone-dn 3 dual-line

cor incoming css-phonethree

Hope it helps.

Thanks

Ovais.

You answered his question and my month long question.  I appreciate the post without the "consultancy" lol.