c6a915b2_10_Free_Softphone_VoIP_Clients__Explanation
[Login Message] "Call failed: 480 Temporarily unavailable" [Solution] Make a test call to a known working number, as a test. [Explanation] 
Dialed SIP number is not on-line at this time.
Softphones | VoIP Softphone Information | 10 Free Softphone VoIP Clients
Explanation