Is there per raw a limit to the number of spells that a bound spirit can sustain simultaneously (apart from the number of services, of course)?
If there isn't, ally spirits inhabitating a small object carried by the mage could work as an an infinite amount of sustaining foci of infinite power. Is that correct?

Each spirit can only perform one service at a time, and sustaining one spell counts as one service.

I have used and seen people ask for simultaneous services, such as Conceal us and Confuse them, or Movement combined with Guard and even Concealment thrown on.

I think it is only going to be limited by fear from such a negative dice pool.

Actually, there is no Raw limit to how many services a spirit can be charged with simultaneously. Allies should not have access to the "Spell Sustaining" service, because it's completely nonsensical.

And I do mean nonsensical. While it would be totally broken for them to be able to sustain all of your spells indefinitely, they actually can't use that service at all because they only count as being appropriate for all of your spell categories (or any of your spell categories) for Aid Study and Aid Sorcery. They technically can't sustain any spells for you.

Spell Sustaining and Spell Binding should not be on the list of available services. In fact, when I wrote the section it wasn't in the list of available options. It got put in as a typographical error during typesetting when a copy/paste got pulled from the wrong spirit section.

-Frank

So, I guess that will be in the Street Magic errata. You know. The one that will be out 'in a few weeks' ....

The justification does not seem very logical to me. Why would a spirit be appropriate to all spell categories for Aid Study and Aid Sorcery, but to none for Spell Sustaining? If a bound spirit is appropriate for a spell category, he can perform Aid Study, Aid sorcery as well as Spell Sustaining for that category, so why couldn't an ally spirit do it too?

Don't misunderstand me, I fully agree that an ally spirit should not have access to the Spell Sustaining service, but your explanation for it is not very convincing IMHO.

That them fragger is already a powerfocus. You want him to be indefinit sustaining foci, have fun. But that's the reason why they don't count as beeing the apropriate type. Gamebalance.

Because it's not one of the five spirit types of your tradition and has the special ability listed on page 105 to count as an appropriate spirit for Aid Study and Aid Sorcery. That special ability doesn't specify any other contingencies and there is no other similar special ability that they have.

It's really quite open and shut.

-Frank