This link will tell you pretty much everything, I only have a few suggestions -

- use the aux line, not the con line, as con doesn't support hardware flow control on most routers and also is very liberal when it comes to security

- try 'modem autoconfigure discovery' first, it works most of the cases and it will save you from configuring chat scripts where you don't need to

- make sure you have 'modem dialin' or 'modem inout' (if you want callback) in your line configuration

- make sure you configure authentication (i.e., 'login' and 'password' or 'aaa new-model') on the aux line or else you will be refused access.

Hope this helps,

Steju