asterisk users - May 2006 - Delete global variable

Hello,

I've got a question to the memory handling of global variables in 
Asterisk 1.2+.

I use e.g. Set(active_${CALLERIDNUM}=1|g) to set a global variable in my 
dialplan. Later I will use Set(active_${CALLERIDNUM}=|g) to remove my 
global variable "active_${CALLERIDNUM}".
Is the Memory space of variable really free?
Or will I rise into a memory problem?

Regards
	Bastian