How to migrate from old PBX to Asterisk?

Hi! I have a client with an Analog NORTEL phone system. They want to migrate few by few to IP Telephony.
So, both PBX need to be interneconnected. How can i do that? Using what hadware? Have you ideas about do this?
Feel free to POST your answers here.

Which Nortel unit? How many extensions/lines on the Nortel unit? Do you have analogue station ports on the Nortel unit?

Either way, you’ll need analog lines on your Asterisk box. You can have it sit between the Nortel and the phone lines where every call comes into Asterisk and can then be directed into the Nortel system or to an IP phone or both. If you have analogue station ports on the Nortel, you can have Asterisk act like extension(s) off the Nortel and into IP phones. If you have both, you can configure Asterisk to be a mix of the two so you can transfer calls around as you need to.


We do this depending on line type using the last method in this page.