Call Waiting on PSTN SPA3102

Hi guys

Right to the fact: I would like to be able to pick-up a call-waiting on the PSTN.

I did install FreePBX Distro and configure an SPA3102.
Everything is working fine except I cannot take a call waiting from the PSTN when already connected to the PSTN.(VOIP->PSTN works fine)

I’m trying to configure Aterisk to flash the PSTN without much success.

I know about the double-flash from the SPA3102 but we have wireless phones and it does not work.

I tried to configure the ZAPFLASH cmd from
But I’m missing something when i try to switch to the call waiting, nothing happens.

I’m a green with PBX, so please be patient with me.

Thanks for any help.