Outbound SMS Creates a Duplicate Chat When the Recipient Replies

[Mike Shintani]

We are using Voxtelesys as our SIP trunk provider, and inbound and outbound SMS messaging is otherwise working correctly.

The issue occurs when a 3CX user initiates a new SMS conversation:

1. The 3CX user opens SMS chat, creates a new conversation, and sends a text message to an external cellphone number.
2. The recipient successfully receives the SMS.
3. When the recipient replies for the first time, the reply does not appear in the original conversation.
4. Instead, 3CX creates a second SMS chat with the same external cellphone number.
5. After that second chat is created, both the 3CX user and the external recipient can continue texting back and forth in the second conversation without any issues.

The original outbound message remains in the first chat, while all subsequent messages appear in the newly created second chat.

This is happening consistently for all of our 3CX users who send SMS messages to cellphone numbers outside our company. Inbound and outbound SMS delivery itself is working; the issue is specifically that the initial reply is being placed into a separate conversation instead of the conversation originally created by the 3CX user.

Has anyone experienced this behavior? Is there a routing, number-formatting, DID-assignment, or SMS configuration setting that could cause the outbound message and inbound reply to be treated as two different conversations?

 

[Charles_3CX]

Hi, in which format do you have your DIDs entered under the trunk? Are they entered in E164 international format?

 

[Mike Shintani]

Hi Charles,

Are you talking about Admin->Voice&Chat->DID Numbers?

They are entered as NPANXXYYYY, not +1NPANXXYYYY.

Is this my issue? We've been setup this way for 3+ years with no voice issues. But, as I mentioned, this SMS duplicate thread has always been an issue.

 

[Charles_3CX]

Enter the numbers as required for this provider in E164 format, as this is your issue, yes.

https://www.3cx.com/docs/sip-trunk/voxtelesys-usa/

 

[Mike Shintani]

Enter the numbers as required for this provider in E164 format, as this is your issue, yes.

https://www.3cx.com/docs/sip-trunk/voxtelesys-usa/

View attachment 52072

Hi Charles,

I made the DID change to E.164 format in 3CX, and that did fix the SMS issue completely. Inbound and outbound texts now stay in the same conversation.

However, inbound voice calls to that DID are now falling through to the trunk’s Default Route instead of matching the DID.

I noticed in the VoxTelesys portal that both my Inbound Trunk and Outbound Trunk number format settings are currently set to “National,” not E.164.

Could that be the reason? In other words, is VoxTelesys still presenting the inbound voice DNIS/CalledNum to 3CX as NPANXXYYYY, while 3CX is now expecting +1NPANXXYYYY?

If so, should I change the VoxTelesys inbound and outbound trunk settings from National to E.164 and then change all of the DIDs in 3CX to E.164 as well?

I just want to confirm the proper configuration before changing the format for the entire trunk and potentially affecting the other DIDs.