[Asterisk-Users] dynamic config

[Andre FAURE]

Hello,

I've been browsing through this archive and the wiki web
but I can't find any info on how to implement some dynamic
configuration like group joining/leaving from the phone,
or programmnig transfers for one extension from the phone attached
to it.
I'm trying to do things like:

   dial *48 : join default group (the one set in sip.conf for example)
   dial #48 : leave default group
   dial *48XXX : join group XXX  dial #48XXX : leave group XXX
        (these I managed w/ a quick and dirty DB trick)
   dial *90XXX : transfers to XXX if call from outside
   dial *91XXX : transfers to XXX if call from inside
   dial *92XXX : transfers to XXX if call is already a transfers

How would you do this? Is the dial plan enough or should some 
programming (AGI, * hacking) be involved?
Sub-question: How would you limit tranfers? Detect loops?

Thanks.