Hi, assume you mean the 4G680 as i can‘t see a reference to the 4G689 on Tenda’s website. If so I have one of these and can confirm the following...
There’s no VoIP functionality in the unit itself.
VoLTE is supposed to be implemented, but UK network support for it is generally currently often limited to certain network supplied handsets/custom firmware/tariffs. It didn’t work on either O2 or Three for me. I used PAYG sims that had both voice and data enabled.
However, fall back from 4G to 3G/2G for voice calls does work, and provided the unit is on the network, a correctly wired phone will provide a (non UK standard) dial tone when the handset is lifted, and the phone will ring (again non UK standard) if the number associated with the SIM is called. Whilst on a call, data transmission is usually slower, so simultaneous calling and streaming may not work too well.
The three PAYG SIM is ideal for testing with calls at 3p/minute, texts at 2p each (the web interface of the router allows text send/receive) and data at 1p/Mb. Obviously once proven, a PAYG SIM with a bundle or a contract SIM would be better for regular use.
Your lack of dial tone suggests that, provided the handset is known working on a landline socket, then you need an RJ11 plug to BT631A socket adaptor.
However, if you have a spare ADSL plug-in filter you can use this as a temporary makeshift adaptor. The filter has a BT style plug, sometimes on a short cable, and two sockets, one RJ11 usually labelled “DSL” “ADSL” or ”Router”
and the other, a BT style socket, labelled “Phone” or with a phone symbol.
Step 1: If the filter is already plugged into a phone socket, disconnect it and anything else plugged into it. YOU MUST NOT CONNECT THE BT PLUG TO ANYTHING whilst you are using the filter as a makeshift adaptor. It’s a good idea to put a bit of sellotape, masking tape or electrical tape around the unused BT plug to prevent inadvertent electrical contact in operation as you may get bit of a tingle, especially if the phone is ringing. Definitely keep inquisitive pets and children away from the set-up!
Step 2: Plug your landline phone into the BT socket on the filter, using the normal cable that came with the phone, and the (grey) cable from the RJ11 phone socket on the router to the RJ11 socket on the filter. Photo below shows how. Note the bit of tape around the end of the BT plug on the filter .
Step 3: Turn on the router. The phone should not immediately ring or make any noise. If it does, then something is wrong. Turn everything off, disconnect it and do not continue. If the phone has a line powered display, that may come on once the router is fully started up.
Step 4: Verify that the router has connected to the network (internet light on, and at least 1 bar on the signal strength meter) Check by connecting to the router wi-fi and browsing.
Step 5: Pick up the handset, you should hear a continuous dial tone, which is higher in pitch than the normal UK landline. You can now try dialling a number. Remember that this is a mobile call so the area code must always be used. The router only supports tone dialling, so if you don‘t hear the tones when you dial, then switch the phone to tone dial, or connect a different phone.
The number you called should ring, and both ends should be able to hear each other. There may be a longer than normal delay between finishing dialling and the other end starting to ring. This is because the mobile network expects the whole number in one go (i.e. on a normal mobile handset, you enter the whole number before you press “send” ), so the router has to wait a few seconds to see if you are going to dial any more digits before it initiates the call.
Step 6: Hang up and return the call. The phone should ring with a single ring.......ring cadence, not the usual UK ring..ring......ring..ring pattern. If the phone has caller ID, this may work, but as again it’s not UK standard then some handsets won’t display it.
If all of that works, then go off to Amazon/Ebay and get a proper rj11 plug to BT socket adaptor. Get one with a ring capacitor otherwise some older phones won’t ring on an incoming call.
If not, post what does/does not work, along with a photo of how it’s wired up and I’ll try to help.