Inboud route, Ring Group and Alert_Info problem

Hi all.

I have a problem with Alert Info.

My inboud route for external calls has an Alert_Info to allow for distinctive ring on Grandstream phones.

When there is an external call, the inboud route give the call to a ring group, where i ring all my phones.

The problem is that one of the phone, a siemens C450IP (DECT SIP phone), doesn’t like the Alert_Info message. It simply does not ring when it receive such a message.

So, my question is, how can i simply customize the .conf files ? Using preferably the xxx_custom.conf files to avoid problems with FreePBX.

Thanks a lot for your help.