I've checked SR4A under "The Action Phase", page 146 and under "Magic Actions", page 179. Also under "Spirit Services", page 186.

The description of Aid Sorcery, page 187, says:
What level of action is it to add Force to a dice pool?

I play a free spirit character and have discussed doing this with my GM. We decided that this was a "this is what you are doing thing". So when you are helping someone, you are using the same action as they are...and probably you have to go first (although we mostly don't worry about it)

So for example your friend Jazz is going to cast a spell (complex action). You take a complex action to aid her, then she takes a complex action to cast the spell
Another example: Jazz is doing a ritual magic. You are casting it too


This is all house rules, but we looked quite hard in RAW and couldn't find any guidance.

SR4 FAQ:
Do the bound spirit services Aid Sorcery or Spell Sustaining take an action to use, or do they happen instantly?

In both cases, the magician must take the appropriate Complex Action to cast the spell, but taking aid from the spirit or passing on the task of sustaining requires no action be spent by either the magician or the spirit; the aid is simply funneled from the spirit through the magician's link to it.

Thanks, Makki, that's helpful.

Here's a question I popped last night in our home game, where I play a Free Spirit. I have the answer for our home campaign, but I thought I'd throw it out here, to see the reaction.

We had assumed that the spirit's Aid Sorcery would take the same level of action as the action she was aiding. Makki's discovery may change that view, but in any case, for an Extended Test like Ritual Spellcasting, we thought extended complex action and for a Spellcasting Test, a complex action. The tricky part came with Counterspelling. Dispelling is a complex action, so no problem there, but Spell Defense is a free action, and usually set ahead of time.

This is where I popped the question. If Spell Defense is a Free Action, then funnelling mana to it being at worst a Complex action could be done at the same time. Could a Free Spirit magician Aid Sorcery for her own Counterspelling (Spell Defense)?

My GM's response: