Is it a 7905G?

http://www.cisco.com/en/US/partner/products/sw/voicesw/ps556/prod_installation_guide09186a0080189f20.htmlUpgrading Cisco CallManager Release 3.3(3)

tested on CCM 3.3.2 with 7960 phone. Unplugged a phone that had no messages. Called and left message. Plugged phone in, registered with CCM and MWI is on.What version of CCM do you have and what is the wireless IP phone (7920?)

yes

A meet-me conference is not active until established by an internal user. Once that is established the external callers may dial the number and join.