obgraham
I can only speak for BA on your question regarding trollies in different galleys. There may be limited space say in a J class galley and sometimes trollies for the second service are kept in another galley where there may be an abundance of space. What usually happens is, after the first service is completed, you would take down the used trollies and bring up the new ones ready for the second service. More often than not, this is done after lights out, which can be tricky, especially if the trolley has been in the chiller for a hours and you are trying not to wake people.
Dot Product
Some airlines do indeed use the call bell for emergencies as a subtle way to attract attention from your colleagues. From a passenger point of view, they may use it to attract attention because of a serious issue, eg: chest pains, while some may use it because they don't wish to leave their seat to have an ad-hoc drink. As a crew member, you're on your own down the back and two call bells go off, you have no way of knowing who needs your help most until you get to the passenger. Personally, I believe they should be placarded for emergency use only.
As F3G says, in a good premium cabin, you should never need use it because crew will always maintain a subtle presence in the cabin (I know this doesn't always happen). In an economy cabin, wherever possible, passengers should be encouraged to visit the galley for their needs outside of service times. This will enable to crew to better serve the cabin as a whole instead of the vocal one or two who take up disproportionate amount of the cabin crew's time, which is not fair to the rest of the cabin.