Yes. In these radios you do that by adding a "wildcard" talkgroup.
In the 668 there is a button to add this wildcard talkgroup in the iScan software on the trunked systems page when you display the talkgroups for a system.
In the 652 you add a new talkgroup on the radio under the system you are after, and then where you would normally enter the talkgroup id, just press the button to move to the right and it puts "wildcard" in there.
As long as you have a wildcard talkgroup in any system on either radio, it will stop on any active talkgroup whether you have it programmed or not.
It is the equivalent of search mode on a Uniden radio.
Mark
536/996P2/HP1e/HP2e/996XT/
396XT/PSR800/PRO668/PRO652