South Korea Number Not Working

SIP
1

Hi,

I have purchased a South Korean tool free number (+82308640190), set up to forward the calls via a sip domain to twilio for inbound calls. The twilio part is tested and working correctly.

Problem: I had a verified domestic test phone call from a real korean mobile number (3 attempts). All 3 returned the same error:

“지금 걸었던 번호는 없는 번호입니다.” (“The number you dialed does not exist.”)

No ringing, no connection — the number is not routable on the Korean PSTN, even domestically.

Could you please:

  1. Confirm whether this number is active and correctly provisioned on the Korean carrier?
  2. Tell me the exact domestic dialing format for it?
  3. If it can’t be made reliably reachable, advise which Korea number type WOULD be dialable by normal Korean mobile users (all carriers) for inbound calls?
2

First, let’s confirm all is OK with the SK operator on this - will update shortly.

Keep in mind there is more info on toll-free dialing formats here:

(will update ASAP though to confirm all is well)

3

any updates on this?

1 Like
4

Hi @Carie_Normand,

We have verified your SK number, 82308640190, by placing an in-country test call and successfully connecting to your endpoint system, south-koreaXXXXX.sip.twilio.com.

Regarding the dialing format, this largely depends on the carrier being used to place the calls. However, the most common formats are: 82308xxxxxx, +82308xxxxxx, 001182308xxxxxx, 00308xxxxxx.

Thanks and let us know if you run into anything.

5

Thank you for verifying the number and confirming the dialing formats - that’s very helpful.

Since my original post, I’ve migrated my endpoint from Twilio to Telnyx. The number is now forwarding via SIP to my Telnyx connection at call-recorder.sip.telnyx.com (using IP authentication with your gateway IPs whitelisted: 46.19.209.14, 46.19.210.14, 46.19.212.14, 46.19.213.14, 46.19.214.14, all on port 5060).

The issue now: inbound calls are showing as ‘Fail / Forbidden’ in my FlyNumber call history when forwarded to Telnyx. I can see the calls reaching FlyNumber with the caller ID, but the SIP forward to Telnyx returns Forbidden.

Could you please:

  1. Place another in-country test call to 82308640190 now that it forwards to Telnyx (call-recorder.sip.telnyx.com), so we can confirm the forward works end to end?

  2. Let me know exactly what SIP response code Telnyx returns on your side when you forward the call, and from which of your gateway IPs the INVITE is sent - this will help me confirm my IP whitelist and authentication are correct.

Thank you!

6

OK, we are getting closer, at least the calls are reaching our system.

The “forbidden” tells another story.

Are you sure [email protected] is the correct SIP URI from Telnyx?

Could it be that TLS is required instead of the usual UDP?

We just updated it manually on our side to TLS, please try now. If you change any settings, the TLS will be lost, so let us know if we need to re-enable that (perhaps with a different SIP URI).

What are the Telnyx logs showing?

7

Thanks for testing with TLS. I checked my Telnyx connection and it’s configured for UDP on port 5060, not TLS - so the TLS change won’t match my endpoint, and that’s likely why nothing is connecting now.

Could you please revert the forwarding back to UDP on port 5060, with this SIP URI:

[email protected]

My connection details for reference:

  • Transport: UDP, port 5060
  • SIP region: Asia
  • It accepts calls from your gateway IPs (IP authentication): 46.19.209.14, 46.19.210.14, 46.19.212.14, 46.19.213.14, 46.19.214.14

Once it’s back on UDP, could you please place one more in-country test call? At the same time I’ll be watching my Telnyx logs live, so I can see exactly what response code Telnyx returns and from which of your gateway IPs the INVITE arrives. That will let us pinpoint the Forbidden issue.

Thank you!

1 Like
8

Thanks for the update, and it’s back on UDP [email protected]

Your earlier tests worked (hence the “Forbidden” in the FlyNumber logs).

Could you try the same way? It seems you called from a phone number 82XXXXXX7654.

9

Thank you for reverting to UDP and testing!

Based on guidance from my SIP provider (Telnyx), I’ve changed my approach. Instead of forwarding via SIP/VoIP, I’ve now set the South Korea number (82308640190) to forward to a regular phone number: +1 606 393 8208 (US).

This routes the call to my Telnyx Voice API application, which resolves the issue we were seeing on the SIP forwarding path.

Could you please place one more in-country test call to 82308640190 now that it forwards to the +1 606 393 8208 number? I’ll be watching my logs live to confirm the call connects end to end.

Also, if you can see it on your side: does the call to the US number connect successfully, and what status does it show in your call logs? Thank you so much for all your help with this!

10

Hi Again,

That works; however, SIP forwarding should work fine. We send calls to Telnyx without issues (plus there is no per minute rate on the forwarding leg of this one).

Thanks for the update. Could you try what you did earlier, as mentioned?