[Freeswitch-users] Presence api for custom function

Hello How can i use the Presence api for my custom application? I would like to set my phone's BLF to set that other phones may or may not be able to pickup the ringing calls. I make a dialplan application for this, and the setting is stored in db. Almost everything is OK, the dialplan application works, BLF's color is changing, but after some seconds it changes back to red. It is obviously because there is not a real phone-ext behind the number of what the phone is subscribing. I thought if i use the presence api, its state does not changes until i send another event for that entity. But it is not true. What can i do? thx