Basically, you could probably put those anywhere you like ; somewhere close to the model will most likely make sense, though.
As an example, you might want to take a look to :
- ZFPlanet : an example of a planet developped with ZF
- Not sure it's finished, but there are several classes, controllers, models, config files, ...
- Which means that going through the code can help (it has, for me, for some things)
- And, especially, its application/modules/zfplanet/models/Service directory
- Which contains two classes.
(Well, I hope that's the sort of thing you meant by Service, actually)
