Just to be clear the rules regarding changing status were altered slightly (see Regent Guide board):
Between Active/Garrison - Immediate change (1 month). Upkeep paid according to NEW status.
To/from Reserve - Change at end of turn. Unit not available for other activities that turn! Upkeep paid according to NEW status.
Note that this means that you CAN bring a Reserve unit to Garrison status to save a bot of money...but it would require another Change Status (and another month) to make it active...so not always wise.
