If you mean multiple registrations, of different devices, all using the same extension number/credentials, then yes. This is called SIP Forking. All devices can place calls simultaneously, and all devices will ring, on an incoming call. You must set an option in the 3CX extension settings to allow the extension to receive more than one call at a time. If you don't and one device is on a call, then any call to the extension number will result in the call going straight to voicemail, or wherever is is supposed to go, when the line is busy.