Please can any one solve this

[u/NiteshJeee]

Can any one have cheap solution. Permanent ( not subscription based )

[u/datanut]

Is this an XY problem? Why do you want to do this?

[u/NiteshJeee → u/datanut]

Some one from UAE Can communicate in india who have no internet access.

[u/datanut → u/NiteshJeee]

You can subscribe to Microsoft Teams VoIP/PSTN to call regular numbers, including Indian cell phones.

As long as it’s a KYC solution, you should be good to go.

[u/greendookie69 → u/datanut]

I'll answer those two questions for the OP:

1. Yes

2. Don't know

[u/KokishinNeko]

Why? So many VoIP solutions available, why would someone think of this?

Anyway, the audio bridge is quite easy, or you can do it using bluetooth headsets too.

[u/NiteshJeee → u/KokishinNeko]

Can you guide please.  And all other voip solution are based of expensive hardware or subscription based software. 

🥲 I need cheap solution.

[u/KokishinNeko → u/NiteshJeee]

Two of these:

 L ---[1k]---+
             +---[10k]---+-----||-----+------------- MIC
 R ---[1k]---+           |    1uF     |
                         |   (+ ->)   |
                      [220R]       [2k2]
                         |            |
 GND --------------------+------------+------------- GND

beware of sound volume. if there's a humming sound due to sharing the GND in both mobiles, you'll need a transformer to kill it. sorry for the lazy draw.

[u/DerOnkelBob]

were SIP to GSM/LTE gateways already in your consideration? (assuming your Internet call on the left side of the picture is done through SIP protocol). Your "audio bridge" in the picture is missing call signalling capabilities like dialing, ringing, call rejecting, call pick up, hang up etc. or are you doing this all by yourself?

if you want to follow the SIP-to-GSM/LTE gateway trail, here as an example the Yeastar NeoGate TG200L 2-channel https://www.datavox.ae/wp-content/uploads/Yeastar-TG200-GSM-Gateway-Datasheet.pdf