1,2 line SIP phone 2,Support 2 SIP Aaccount 3, Support Transfer calls function/Three-way conference/Call waiting fun Important: It can store two SIP accounts, press 1# key, choose the first SIP to call; press 2# key, choose the second SIP to call...For useful:1, the first SIP Account no balance, you can press 2# key to choose the second SIP Account to call...2, the two SIP Account from two ITSP, ...