Hmmm...
Whilst not strictly standard r/t, I have a unwritten system.
if I have co-ordinated your frequency transfer, I will say;
"contact xyz, 123.45. ba-bye"
if I havent, and you're freecalling the next unit I will say;
"freecall abc, 123.45. ba-bye"
If I am sitting next to the person and I slide the flight progress strip to them, I will say;
"contact tower, 123.45."
Im my opinion, (no offence to GA/Pro pilots) it helps distinguish the difference between a end to the unit's service and just the transfer to a different part of the unit. (*does that make sense?)
On the other side of the coin;
Manners cost nothing when it is quiet, but when its busy manners cost seconds. When I stop being polite, pilots hear the change of tone in my voice an expedite the read-back. I feel it may even give pilots a clue about a controllers workload at any particualr time. Remember, just because you cant hear any r/t chatter doesnt mean we're not rushed off our feet.
Bri.