You think a customer can be upset when a camera isn't working, Ha, wait until their phones are not ringing.
We began in Voip in 2005, invested heavily in asterisk expertise, lost our shorts the first year, realized we are better at sales and support, but poor as an engineering company. In 2006 we chose PBXnSIP, later absorded into sister company (SNOM), and then spun off to the original founder, and chief architect, Christian Stredeke as Vodia. great product, we've integrated with about every SIP host, Broadsoft, Cisco, and some oddball carriers. 3CX, is another software only product thats been around a while.
Polycom dominates in the hosted PBX business, and both products support them well, However, we only did Snom 3xx handsets, their DEC wireless, and conference phones.
We left the VoIP business 2 years ago, but still support a few hundred handsets with clients using all of our Managed services, IT, cameras, and PBX's... No longer offering PBX solutions.
SIP trunks - selling and supporting SIP trunks on broadband connections in the BYOB "bring your own bandwidth" can be extremely risky. You'll have to monitor numerous points on the carriers network to catch latency issues, and go to battle on behalf of your client when issues occur, and the broadband providers will tell your clients they don't support BYOB voip, and make you the fool. Getting a MPLS T1 from the ITSP will be expensive, and will not be cost competitive with a traditional T1, but then you'll use TDMA/SIP gateways and the better ones are Epygi, Patton, and Sangoma.... (used them all, prefer Epygi for their support.
In my opinion after 8 years in Voip, the best Voip distributor is Novus, and I've worked with many.