Hi!

The idea of IPMA is to allow managers and assistants work together. For example, an assitant will be able to intercept calls that go to a manager's phone and the manager can user couple of modes such as DND and iDivert. The assistant has a GUI interface to monitor the manager's phone.

Basically IPMA can be configured in 2 ways:

-Shared line support: here both, the manager and the assistant share a same DN.

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/6_0_1/ccmfeat/fsipmasl.html

- Proxy line support: A proxy line specifies a phone line that appears on the assistant Cisco Unified IP Phone. Assistants use the proxy lines to manage calls that are intended for a manager.

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/6_0_1/ccmfeat/fsipma.html#wp1071190

HTH, if it does please rate :)