Dear Marco. Yeah, Agree with you. The SIP implementation is EXTREMELY finnicky. I've been trying it against different devices / SIP servers and it has been very hit-or-miss. You have two modes though, one where the Dahua acts as a SIP server itself so that other devices can register to it and the second one where it acts as a SIP client and registers on a SIP server. On the first case (where dahua was a sip server), I managed to register a Windows version of Zoiper and it sort-of worked. But trying to register my gigaset device was an excercise in frustration and it never worked. On the second case, connecting it to an asterisk server, I saw it behave a BIT better. But it still kind of tricky... and you have to tweak things like DTMF enconding (I think you have to move the DTMF signalling to the RTP traffic instead of a SIP signal (or vice-versa)) for the door opener to work for example. I was not planning on using it with a cloud provider on my case... my main idea was so that I could integrate it with a local asterisk IP-PBX and anser the door from the different IP phones in the house.