Call waiting

I searched this forum but I was not able to find anything regarding my problem. Could be that I’m looking for the wrong keywords since I’m not really sure if the terms in English are the same as my native language Dutch.

I connected an IP DECT system to FreePBX, FreePBX itself is connected to another PBX via SIP trunking.

All works well, except that if someone gets a call on a DECT handset and another call comes in (you hear the call waiting beep), from that moment on the R button will only switch between those 2 calls. It’s not possible at that moment to reconnect any of the 2 calls to another phone. Only if one of the 2 calls ends it’s possible once again to reconnect the remaining call. This problem only applies to the IP DECT handsets, the normal phones connected to the PBX directly don’t have that problem.

It’s a very odd problem, I hope that someone can give me some pointers on that!

Thanks

I am using a Digium card with three FXO ports and one FXS port, connecting to the PSTN. Currently only two lines are in use and both lines have call waiting options enabled via TELCO. I can hear the tone in the handset when another call is trying to come into the system, but cannot find a way to flash the new call. Put the current one on hold and accept the new call. Since the Digium card is announcing the second call to me, i assume it is not the card configuration. So what am i missing in FreePBX? Any suggestions?