I can't call SIP URI "firstname.lastname@example.org" with softphone. do 3CX system allow SIP URI calling inbound and outbound from/to another voip provider? I want call with SIP URI to another voip provider and I want receive calls with SIP URI from another voip provider. If this is possible, you must add "address book" for SIP URI in 3xc system for voip ATA device. voip ATA device can call SIP URI with short cut phone pad (#01) or with extension number ( email@example.com). you add sip uri field extension page. example: #firstname.lastname@example.org or email@example.com Softphone can call always with sip uri. thanks.