Differentiating between two sets of phone lines

We have analog trunks that are used by our company. There is a main number that is rolled. We are interested in getting a new set of analog trunks for another company we plan to start.

The new lines will continue to go through our Asterisk setup but when the phone rings we want to know which company the caller is calling.

What is the simplest way of doing this. We have Polycom IP600 phones.