asterisk users - Dec 2011 - How to count ongoing calls from the dialplan

Hi,

When I need to route calls depending on the number of (incoming and
outgoing) calls a SIP device is currently handling, I mostly use
function SIPPEER and its curcalls option.

I can read and there references to function GROUP for the same usage,
but I intuitively thought that though this method also applies to
non-SIP devices and a large range of asterisk versions, it would
require more work from me to tune my dialplan.

Which method would you recommend ?
Suggestions ?

Regards