I was nervous about 2talk after reading all the bad feedback but I have to say I have nothing but admiration for the service they provide. SIP setup was easy and having setup a raspberry pi astericks server in the office, everything is working smoothly with great call quality.
For a small business you really can't beat a few second hand Grandstream SIP extensions and a raspberry pi Freepbx setup that uses about $6 of power each year. Total setup cost of 4 extensions & 5 line exchange $300NZ.
I have rung the 2talk help line on 2 occasions,one of which was today and today they answered straight away and were very helpful You can't really ask for more.