Part of Elastix is re-packaged FreePBX (also separately accessible) and all web based. Chose it because of the extra features (mainly HylaFAX). Was very easy to config and provision with.
At first I also wasn't too sure about mweb as a voip provider, but was worth the try as there is no fixed monthly / initial setup costs. Must say I am impressed by the call quality and (lack of) latency. Haven't attempted porting my Telkom numbers across as it's used for outgoing calls only so not sure if they offer that. Personally I'd go for an
0861 maxicall number from Telkom & just point it to the sip number, that way if a better provider comes along in the future it's just a case of rather painlessly updating the 0861 destination.
Regarding WISP, I'm with Amobia on the 1.5GB, 1mbit symmetric unshaped capped account for R199 p/m, haven't tried saturating it with calls, but it handles my 5 simultaneous without any problems. There is are some calculators around such as
this one. Theoretically one g729 channel uses 8kbps symmetrical bandwidth, if you divide the line speed into that it should give a rough idea of what it can handle. I also chose Amobia because they break-out at Mweb. Average ping is 20ms to the sip server compared to 18ms on the business uncapped ADSL.
I use the A510IP (one base, two handsets) as it handles 2 simultaneous calls. SNOM M9 can apparently handle 4 simultaneous calls, but I find the build quality, range & battery life to be inferior by far to Siemens.
Regarding branches, there are a few options:
- Keep existing pbx, add sip gateway to free trunk lines, use sip for least-cost routing and inter-branch routing.
- Keep existing pbx, get a hybrid gateway (or mypbx) connect the gateway in series with the existing pbx.
- Replace pbx with sip
First option is the cheapest and easiest to implement, if the existing pbx allows trunk-to-trunk routing it can forward calls to another destination.
Second option is more complex to setup but is still cheaper than replacing a whole existing system. As all lines will trunk through the gateway you will have full control over how to route calls.
Third option will be more expensive depending on how it's implemented, but you will have complete control over the whole system.
If you require full inter-branch routing (ability to forward a call from extension X at point A to extension Y at point B) then you will have to trunk the branches to the head-office and/or to each other. You must first look at deploying a separate WAN/VPN to keep the pbx's off the direct internet for security purposes. Depending on how big your business is something like an MPLS network with a hosted pbx (server managed and owned by you in a datacenter) may be a better option.
Alternatively if all you require to be able to do is forward a call from user at point A to reception/IVR at point B then rather keep it simple and use the free on-net calls of a sip provider. (i.e. each branch has it's own sip account with the same provider, calls forwarded between branches to their respective sip numbers are free)
G729 licensing gets you an official version of the codec, having tried both the free one and the paid for, there is definitely better performance from the paid version (it includes a benchmark utility to determine which version of the codec will work best with the architecture of the sever).
If management doesn't want to fork out to replace the existing pbx just get a gateway to interface into it (set the bri gateway's ports to NT mode) Have done this at one site and it works great, although did require some dabbling with settings on both the existing pbx and gateway to get working as required.
Have a wireless link between two offices (3km) via a high-site (also no los), using Ubiquiti nanobridge kitt and it works very well routing both voice and data.
