Softphone failing when calls originated from certain mobiles

[Farking]

I'm having an issue that is becoming very problematic.
We recently switched over to a VOIP system after I recommended 3CX to our work after working with them on another company many moons ago.
Here is the issue we are having:

We have calls come into our reception extension on our 3CX windows app, we also have the 3CX softphone installed on an iPhone that shares this extension, we use this as a speaker to know when calls come in and also we use the iPhone so reception can answer the calls when doing other duties away from her PC.
We can answer all calls using the Windows app, without issue. But when we try and answer the calls using the 3CX softphone on the iPhone it will fail.... but only sometimes.

After doing some more testing I started to realize it was when I call on my mobile phone, We can answer the calls using the softphone if anyone is calling from a landline. We then went through and testing with all the different mobiles staff had in the office, and it seems to work fine on most of them (as in we can answer the calls on both the 3CX windows app and the 3CX softphone without any issue) but when I call on my mobile phone (which is an OnePlus 8Nord) it fails. My phone is dual sim so thought maybe it's the carrier with the issue but the same happens on both mobile networks I subscribe to. We have other androids in the office and they seem to work fine.

Now we are finding that if we answer calls on the softphone we have some that fail and some that connect as normal and all calls from landlines will work as normal. So we are assuming that this issue is the same issue I'm having when calling from my mobile where the softphone won't answer. And other customers of ours having android phones and getting the same call failed issue when we try to pick up a call on our softphones.

 

[cobaltit]

So it's a bit confusing so let's simplify this. First, more info on your setup:

https://www.3cx.com/community/threads/information-to-provide-when-requesting-help.67558/

Second, please confirm if this issue is for calls from mobile devices via the mobile carrier (not 3CX client) and when answered ONLY on the iPhone and not when answered on the Windows client.

And is the SIP trunk from a certified provider?

 

[Farking]

Thanks for your reply,

• 3CX Version, Standard Annual 16.0.9
• Server OS, Debian 9 / Windows Server 2012 R2 / Raspberry Pi
• Is the 3CX Server Hosted and where? Provided by our auth Reseller
• IP Phone Make/Model/Firmware N/A
• Provisioning Method:
• Trunk Provider or Gateway Make/Model Kiwivoip
• Has the Firewall Checker passed: YES
• Are custom Phone Templates being used: NO

Please confirm if this issue is for calls from mobile devices via the mobile carrier (not 3CX client) and when answered ONLY on the iPhone and not when answered on the Windows client. Yes this is correct

Our SIP trunks are from a Certified Provider (Kiwivoip)

 

[ChrisC_3CX]

This is a very strange issue and I can't see why the Mobile App would selectively have a problem for incoming calls arriving from your specific GSM number(s).

My thoughts are either that something is happening on the provider side, or there is some strange configuration in the PBX.

My advice would be to contact a 3CX Partner to help you pinpoint this.

As a test though, I would do the following:
Create a brand new extension on your 3CX, then register the Receptionists iPhone there. Then point the DID number to the new extension. Call again from your GSM Number using your OnePlus 8Nord.

Does it still happen? If no, it is probably something on 3CX that is configured in a very strange way. If yes, I would lean towards provider.

A proper troubleshooting though I think is required here.