Hi Steven,

Hope all is going well with you :) The Feature that you are looking for is called "Join Across Lines". Sadly this is not available until CCM 6.1

Cisco Unified Communications Manager 6.1 introduces two new features that help increase collaboration and improve access to coworkers. The first one is the Join Across Lines feature for connecting multiple calls or conferences and the second is a Single Button Barge feature that allows authorized users to enter a call as an additional party by pressing a single key.

Join Across Lines

When the Join Across Lines feature is enabled, users can join calls across different lines that appear on their phone. The feature enables the executive staff and other users to swiftly connect different parties into a conversation.

A further refinement of this feature is a "join-pending" mode. This mode is invoked through a softkey when there is only one joinable call in progress. In join-pending mode, the primary user is prompted to join more calls and may complete the joining process as additional calls come in or are dialed out.

With the Join Across Lines feature, conference chaining is also possible. When two or more calls are already in a conference, users can chain together conference calls that appear on their phones.

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_data_sheet0900aecd806e86dd.html

Join Across Lines

(SCCP phones only)

Allows users to apply the Join feature to calls that are on multiple phone lines.

http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7961g_7961g-ge_7941g_7941g-ge/6_1/english/administration/guide/7961usr.html#wpmkr1056426

Hope this helps! Sorry man!

Rob