It doesn't matter who is more or less experienced in anything; the power of a forum lies in information sharing!
The links and options you have brought to the table - while perhaps simpler - are incredibly useful, perhaps more so than you realise. Thanks again!
So ... over the weekend I did some research at my parents' place using the D-Link DWR-956M router that Telkom dropped off on the SmartVoice contract. The device is a lot smaller than one might think, about the size of an A5 book and about 1" thick. Its most imposing feature is the four relatively large antennas, two for 4G/LTE and two for Wi-Fi :
View attachment 757518
The DWR-956M has dual-band Wi-Fi and is fibre-ready; there is a WAN socket (for a feed from a fibre ONT) on the back panel, along with a single RJ-11 socket for plugging in an analogue phone.
The router is somewhat customised for Telkom and the firmware has a 'setup wizard' that is actually quite user-friendly, it guides the novice user through a basic setup of creating UserID/Password combo for the device's login page, doing a basic (wired) DHCP network setup and setting up Wi-Fi. There is a SIM tray on the underside that takes the Telkom-supplied 'SmartVoice' (or other) micro SIMcard:
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After running the setup wizard, the internet (data) side of the things worked pretty much out the box. Voice calls made from an analogue phone (corded or cordless) plugged into the back phone socket worked fine too.
Accessing the router's "advanced settings"page revealed a 3-way setting that allows voice calls originating from the analogue phone socket on the back to be routed in one of 3 ways:
- 'CS' ("Circuit-Switched") - meaning voice calls are carried as a normal cellular call (GSM or 3G) over a dedicated digital voice circuit;
- 'VoIP' - meaning the call will be carried on a SIP/VoIP link over the router's 4G/LTE or fibre WAN connection;
- 'VoLTE' - meaning the call will be carried using the dedicated VoLTE protocol over 4G/LTE.
- 'Auto' - like the name says (this was the default setting as Telkom deployed the device)
The router's front panel has a few indicator LEDs; one of them (the rightmost one in the pic below) indicates which phone mode is in use : solid green for CS, blinking green for VoLTE and solid blue for SIP/VoIP:
View attachment 757540
The light was solid green indicating CS mode, ie the device is routing over a normal cellular voice circuit. Changing the voice call setting to explicit CS on the router made no difference, ie phonecalls still worked fine.
Conclusion : Telkom is routing voice calls originating from the back-panel RJ-11 socket as normal cellular (GSM or 3G) calls. At least for now, they are not doing anything special (like using VoLTE).
My parents already had LTE internet using a ZTE MF286 router that was supplied previously under an MWeb-over-CellC contract. That contract was recently migrated to an MWeb-over-Telkom contract due to CellC exiting the fixed-wireless market. So we already had a working MF286 setup and that device has some nice additional features including a lithium-ion backup battery and
two RJ-11 analogue telephone sockets (the D-Link DWR-956M only has one).
After moving the Telkom SmartVoice SIMcard from the DWR-956M to the MF286 and changing a few settings, I was able to make phonecalls and get internet on the MF286 as well - no problems. My parents used to have two incoming analogue telephone lines, one feeding a set of 3 DECT cordless phones and the other feeding a wired bedside extension/fax (yeah, I know). I plugged both RJ-11 cords into the MF286's two RJ-11 sockets and all worked fine. Calls originating on either of the analogue phone sockets are carried over the same cellular circuit and appear to the called party as originating from the same number, which in my parents' case was the number ported from their old landline. Happiness.
Subjective impressions so far, using the ZTE MF286 router and an old Siemens analogue corded phone and 3 x Panasonic DECT cordless phones :
- Audio quality from all the analogue phone sockets is excellent - as good as any normal 'good' cellular call;
- Call volume is excellent at both ends;
- Dial tone sounds a little different (no warble, just a long, continuous tone);
- It takes a little while longer for a dialed call to connect and for the router to recover (give back dial tone) after a call is terminated - about 10 seconds for both;
- The voicemail number on the Telkom cellular network (181) is different to what it was on the analogue landline network and voicemail needs to be set up from scratch.
Nothing too much there that the elderly folks can't deal with. Happiness again.
So, the superfluous DWR-956M (with its horrible 2-year contract) will be returned to Telkom this week; and the 2nd voice/fax line my folks had will get cancelled.
So : if you already have a 3G or 4G/LTE cellular modem/router that has analogue phone support, it seems this can be used directly with the SmartVoice contracts with no particular issues. It is now proven to work with the ZTE MF286, it is almost certainly possible with the Huawei B315 or B525, and I have done something similar in the past with a Huawei B593 (2 phone sockets).
If you are starting from a clean slate, it will of course also work with the D-Link DWR-956M that Telkom supplies with a 2-year contract. But it may be a better option to purchase a router and go month-to-month, avoiding the contract with Telkom. With the uptake of fibre internet, there are plenty of these types of routers on the 2nd hand market.