1st example:
A free spirit casts improved invisibility on someone, then dematerializes but continues to sustain the spell, so both can sneak somewhere (the astral form just following the invisible person's aura. Does that work?

2nd example:
A magician casts improved invisibility on someone, then begins projecting but continues to sustain the spell, so both can sneak somewhere (the astral form just following the invisible person's aura. Does that work?

I found nothing in the 4A core rulebook's magic chapter which would forbid this.

exclusive actions or whatever they were called in 3rd edition are gone, if that's what you're asking.

in regards to those specific questions, I'm pretty sure they are both quite possible.

As far as I know when it comes to magic, both examples are possible.

You don't need to maintain a line of Sight to sustain a Spell .Only during casting thats when You have to see the Target (and You have to be on the same Plane)

HokaHow
Medicineman

I will add quadruple confirmation. Both of those actions are legal in SR4.

That's indeed what I'm asking, although I couldn't remember the technical term.

Thank you all!

When I was playing 3rd ed. I used to say:
Bleeding is a Free Action, but dying is an exlusive one.
(Can't say that in 4th ed anymore)

with an exclusive Dance
Medicineman

Quintupled. You just have to be physical to cast a Physical spell - there's no requirement that you stay Physical.

So to use this to its limits...

A force 6 spirit of Man can "know" two spells that you know.
You keep summoning/dismissing until you get 3 services (rest all the stun damage away).
You Astrally Perceive to become dual-natured.
Your spirit casts both those spells on you, and sustains them for free
You stop Perceiving, but the spells remain on you? (no longer in Astral line-of-sight)
Spirit follows you all day (until sundown) because you still have a service left.
You keep 2 free sustained spells as you go about your business.

Works?

Nope. Spirits will only sustain a spell for a limited time and it has to be a bound spirit. The time limits is spirit force in combat turns per service. Furthermore, the spirit needs to be manifested if you want it to cast a spell with the Physical descriptor. Only mana based spells can be cast from the astral. See pg 187 SR4A. They may have changed this for 5th edition but I doubt it.

EDIT: Missed the spirit of man part. Yeah they can cast and sustain as a single service. The basic thing to remember about spells is, you can only cast on something that is on the same plane as you (astral on astral, physical on physical) and only mana based spells can be cast on the astral. Improved Invisibility, for example, is a physical spell and therefore a spirit would need to manifest and cast it on the physical. The spell can't even be cast in the astral.

As far as I know, as long as both are Mana spells, yes. If either is a Physical spell, then going Astral is not necessary as the spirit will have to Materialize to cast them (this won't cost a service as it's part of the request to begin with).

As continuous use of a power has no defined limit, short of the next sunrise/sunset, then you really don't need a third service to keep the spirit around. At zero services it will still stay around as long as it is performing a service for you (it can't leave till the job's done). If both spells are disrupted by any means (Counterspelling, wards, BGC, etc.), then the spirit splits unless there are more owed services.

Don't forget that casting those two spells does cause drain on the spirit, and depending on the usual factors it is possible that the spirit could disrupt itself from the Drain. I tried looking a bit, but I don't know for certain if the spirit will suffer the DP penalty for sustaining or not (I would think so as this is otherwise a spell in all aspects).

And I'm probably forgetting a few things in all of this, but intentionally omitting everything about walking around with magical auras on you for a day.

Added: Yes, bound spirits are required for sustaining spells that the summoner has cast, and there are additional limits on that. As a power for a Spirit Of Man, Innate Spell falls under the "Continuous use of a specific power..." part under Spirit Services on SR4a, page 186 (as far as I understand things here).

it's worth noting that wards are fairly common. not so common that you'll run into one going into a stuffer shack or anything, mind you, but for a shadowrunner at least, wards and other astral barriers are a fairly common thing to run in to, so you can expect to have problems with your plan if you're actually going into anywhere remotely secure.

you will also need to have the spirit stay relatively close to you, since it is unbound, which means in addition to those spells potentially being removed each time you go through a ward, there's a chance the spirit won't be able to make it through the ward either, which can be a problem.

Works (potentially) if the Spirit is an Ally Spirit (and the Spells are Mana Based).

It's a Spirit Power, not a spell, so no sustaining penalties apply.

innate spell gives you the ability to cast spells, and knowledge of a spell. it doesn't actually let you manifest the spell as a spirit power.

Hrmm, interesting.

Although, by the text it refers to many parts of spellcasting in general (skill, target, drain, ect), but does not implicitly list Sustaining penalties as per normal spellcasting. Obviously it is inferred, especially as in the duration of the Power it lists "Duration: per spell," but there's enough there for an argument to be made for Innate Spells not having Sustaining penalties.