In the outgoing case: at least one called user has been alerted about the call (a SIP 180 (Ringing) packet or equivalent has been received) but none have answered, so the call cannot go to Accepted (use Ringing to determine which members have been informed and which haven't, if you care).
UIs SHOULD produce a dialtone for outgoing calls in this state. In the incoming case, the local user should be informed of the call as soon as the call reaches this state (and SetRinging should be called to inform the CM that this has happened, so that it can relay this fact to the caller using a SIP 180 (Ringing) packet or equivalent).