Unable to Transfer Incoming PSTN Calls to External Numbers via FreePBX + Grandstream HT503

FreePBX Endpoints
1

Hi everyone,

I’m setting up a call system using FreePBX connected to a Grandstream HT503 (FXO port) that receives analog PSTN signal from my fiber modem via RJ11.

The call flow is as follows:

  • An external caller (from the public phone network) dials my landline number.
  • The call reaches the HT503 (FXO port) and is passed to FreePBX.
  • From FreePBX, the call is routed to an internal extension.
  • The extension user answers the call and tries to blind transfer it to an external mobile number (via the same HT503 FXO line).
  • At this point, the call fails or returns to the IVR.

I’ve tried configuring the Follow Me module with the “Outside Calls Fixed CID Value” and also tested various CallerID options. I can see the Local channel is initiated, and FreePBX attempts to dial out, but the external leg of the call is either dropped or not connected.

Outbound calls from extensions to external numbers via the HT503 work fine. Only call transfers (from an incoming PSTN call to another external number) seem to fail.

Is this a limitation of the HT503 or a setting I might be missing in FreePBX or the ATA?

I’m traveling with my Grandstream setup and would love to get this resolved remotely if possible.

Any advice, experience, or configuration tips would be greatly appreciated!

Thanks in advance.

2

You can’t do that because you only have one FXO port that is already in use with the incoming call, so you can’t use it again for the outgoing call.

1 FXO port = 1 call

You can’t have more that one active call on a single FXO port at any given time.