Parking lot support is implemented in 2.10.
You need to create a context in asterisk's dialplan:
[fop2-park]
exten => _X.,1,Set(ARRAY(RETURN_EXTENSION,RETURN_CONTEXT)=${CUT(EXTEN,:,1)}\,${CUT(EXTEN,:,2)})
exten => _X.,n,ParkAndAnnounce(PARKED,,Console/dsp,${RETURN_CONTEXT},${RETURN_EXTENSION},1)
exten => _X.,n,Goto(${RETURN_CONTEXT},${RETURN_EXTENSION},1)
exten => _X.,n,Hangup
The button definition for parking is like this:
[PARK/default]
type=park
extension=700
label=Parking
context=parkedcalls