Hi Cristian,

With the 7931, the method that you are using is an excellent way to overcome the "built-in" Max calls per line button restriction;

This is actually a restriction on the 7931 :(

Conrad is a product manager in Cisco IP Communications. He is responsible for many aspects of the phone user interface for the Cisco Unified IP Phone 7970G, 7971G, and 7931G models.

The 7931G was developed for the key system market, common in the retail and commercial space. It was developed in conjunction with the CUCME product team, and many of the features were implemented with a key system in mind.

A single call per line/button is the intended operation, with transfer and conference taking place across lines/buttons.

We wanted to have a large number of line keys, in a small form factor, for retail environments. In this environments, people tend not be so interested in voicemail, directory, and settings, or a large display screen. There is more interest in having a simple User Interface, with a line key light up when the call comes in, and very clear options to hold, transfer, or redial a call.

The phone required some changes to CUCM, and CUCM 6.0 is the first version to support the 7931G. The recommended configuration is to set any DN to have a max-calls of two, and busy-trigger 1, to operate in a key system style of operation.

From this Ask the Expert Event;

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified Communications and Video&topic=IP Telephony&CommCmd=MB?cmd=display_location&location=.1ddead63

This document shows how to use Partitions and Calling Search Spaces to configure multiple lines on one phone with the same DN. It is assumed that the user wants all incoming calls to start on line 1 and forward to subsequent lines if line 1 is busy.

Configuring a Single Dialed Number on Multiple Lines

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a008009409c.shtml

Hope this helps!

Rob