If I can summon Task Spirits (p 98, Street Magic) they have the optional power of Skill. There doesn't seem to be a restriction on having to know the skill you're giving the Task Spirit (like there is if you give a Spirit of Man an Innate Spell.) So if my Possession based mage summons up a force 6 Task Spirit, gives it a couple of skills that the summoner doesn't have, then has the spirit possess him, shouldn't that give the character a couple of free level 6 skills to throw around?

Also, there doesn't seem to be any restriction on the skill level listed. Does a force 12 Task spirit have a skill level of 12?

Limited to only Technical (not sure about the hacking type skills though, what with the no AR clause for spirits) and Physical skills, I know, but that does make for a pretty good summonable medic. Just follow it up with a Spirit of Man with Heal.

Yes, having task spirits lets you have access to pretty much any technical skill you want, though having the spirit possess you doesn't just give you free ranks in the skill(remember if a spirit possesses you they are in control of your body, you just give them orders.)

A spirit would be unable to hack due to the fact that they cannot perceive the virtual world(and most GMs would rule that a spirit would have no way to know hacking skills in the first place).

yup, you pretty much have it dead on.

What about skill level limits? Is it just force?

Yes skills are always at force rating.
I would like to point a couple of things:

Manifesting spirits see trough astral perception so they cant use any kind of AR (they would only see the astral shadow of the display and having no body they can't manipulate AR glowes), Materialized and Possessing sirits can (thanks to AR goggles and glowes) but can't use simsense and/or DNI (I highly suggest to use the just-1 matrix-IP-in-AR opzional rule from Unwired); as for having the skills Street Magic states that task spirit can recive any physical or technical skill in place of an additional power (no magical skills except, maybe, for arcana if said skill is considered technical), so it boils down on how you consider matrix skills (in my hopinion they are technical).

Possession traditions are great but for situation in which no combat materialization is better for multitasking reasons, you can have just one body.

I've read in Street Magic a Metamagic Technique which allow a summoner of a Possession tradition to "share" skills, attributes and control of the body with summoned spirits who posses him.....

Channeling.

So with Channeling, you can have acces to the skills of the siprit you summoned. Task or Guardian... and you keep control of your body so you get your magic skillwire....

Yep, Channeling is awesome. I still don't trust my GM enough to have a possession tradition, because he likes to be 'creative' with the spirits.

Channeling allows both the spirit and the host to control the body, but not at the same time. So, if the spirit is doing a task with its skill, the possessed mage could not be doing another physical task.

It isn't clear to me whether the vessel/host mage could cast a spell while the possessing spirit did something else. The biggest issue would probably be whether the spirit was directing the body's eyes in the right direction. A GM might be inclined to assign some kind of negative dice modifier, similar to that from sustaining a spell.

Presumably the mage could set the possessing spirit to a task or set of tasks, and then project astrally, thereby allowing simultaneous action, albeit in different planes of existence.

Peter