Grandstream HT503 and Freepbx

Hello Guys

I have 2 issues with the HT503 and Freepbx and I am not sure if they are related.

On my outgoing calls I cannot I have a busy signal of about 4 seconds between calls.
My second issue is that my incoming calls seems to hangup and rings again,I can see it on the Cli
that is is hanging up and dialling again.The caller hears the normal ringtone but the extension
rings,stops,rings every one second.

Please assist

you have to check the 503 from GUI,make sure the busy tone detection is enabled.