Finally managed to get an update on the timeout issue. Took me a while to reach out to them. The updated firmware files (there are 2) have been uploaded to the same Github repository:

https://github.com/Yuno-Tesu/Tp-Link-XC220-G3v-v2-Firmware

Take care to upgrade in stages, i.e, upgrade to firmware version 1 first, then second, then third. Do not upgrade directly to the third one. The telephone works without timeout currently. Even though it has been a long while since the last discussion, I hope this helps someone.

Edit: I was unable to access the router configuration page after the final firmware upgrade over ethernet. Can still access it over WiFi connections. I'm not sure if this is an issue on their end or if it will be fixed.

  @mahat  pon register karte time epon ya gpon aata ye dekhe

  @tusharsnn Thank you for letting me know that it works. However, as  itsroshanali pointed out, there is a timeout. I'm not exactly sure what the maximum cap is. It should, but does not automatically reconnect after the timeout. VoIP will work after restarting the router. This is a less than ideal situation. I cannot contact support for an extended period of time because I had to relocate. Will let you know if I get a response when I can contact them again.

If you happen to contact them and get a fix, I'd really appreciate it if you posted it to the forum as well. ^ ^

@Yuno-Tesu Thanks for sharing the firmware. I did manage to get VoIP working after leaving it non-functional for months before I discovered your repo.

The steps I followed:
1. Download and apply the new firmware from https://github.com/Yuno-Tesu/Tp-Link-XC220-G3v-v2-Firmware/blob/197af8bb95a8713dc10d24aafdfb38f994e8097c/XC220-G3vv2_1.11.0_0.8.0_UP_BOOT(240612)_2024-06-12_20.14.45.bin.
2. Delete the old VoIP interface setting from Network > Internet.

3. Create a new VoIP interface with the same settings. (Service type: VOIP, Vlan Id: 1831, IP: Dynamic, Interface Binding: VOIP). 
4. Make sure the VoIP interface status is 'connected'. (If not, make sure the interface settings are correct in the last step).

5. Go to Telephony > Telephone Number.

6. Delete all the existing configurations.

7. Add a new entry with the correct settings. Ask your ISP for Registrar address, authentication id, and password for VoIP. Choose "Other" as the Telephone Provider for BSNL connections.

This should be enough to get VoIP working.

  @Udhaya could you please re-upload. Link not working.

  @Yuno-Tesu did u found any solution for voip
And (thanks for the stock software that better than bsnls frimware and its voi ip timeot in an hour i think). if u found any solution reply

  @sp6035 I think this is quite misleading. Do enlighten us which application you're speaking about. It is true that BSNL is hesitant to work with TP-Link routers, but the way you say it, the routers no longer being supported, would imply that current users will face problems as well. This is not the case.

BSNL uses D-link routers in my area, which is arguable worse in terms of configuration and control. If you're ready to setup the router (Tp-Link) yourself, the internet works flawlessly. However, the voice part is not quite as smooth. There are issues with timeout in the VoIP settings.

  @mahat 

Setup Guide for BSNL FTTH: https://youtu.be/o8zBrZZUf9s​​​​​​​

I have bought this router with firmware no. 1.8.0 0.8.0v6062.0 build 230720 Rel 48094n and hardware no. XC220-G3V v. 2.0 000000 three weeks back for my BSNL FTTH connection. I have configured both internet and VoIP on my own . I had to ask bsnl to refresh the MAC address of my new router on their system after which the router is working flawlessly for both internet and telephone. The configuration gui of tp-link is completely different from my other syrotech router which is generally used by bsnl service providers so I had to figure out how to transfer settings from my old router, but I was able to do it suceesfuly . This router is extremely stable and the gui is considerably simpler from other chinese white label routers such syrotech, digisol etc. . also you can control the router remotely using the tether app from tp-link. As far as I know this is the only mainsream brand fiber router currently available in indian market.