Ancient History's metamagics page says that a lot of them are taught by spirits. How does that work? I thought metamagics were learned through initiation; am I missing something? And how would a spirit teach another spirit metamagics?

Also, would you be able to do services for a free spirit in lieu of karma payouts? Like, teach it spells or something?

Spirits don't need teachers to learn spells like metahumans do, they just spend the karma, hit the target number and bang, they know it.

Some metamagics are similar or identical to spirit powers, and a spirit who has that power can teach it to an initiate in the same way one initiate can teach another. Spirits do not teach other spirits metamagics, they gain new powers as they advance in Force naturally.

However, doing services for Free Spirits in lieu of paying karma is toatlly allowable, subject to the particular spirit and GM whim.

When you initiate you gain the ability to learn a metamagic, you don't learn it automaticly. You still have to be taught by someone who knows it or by a spirit with a similar power.

Certain spirit powers are similar to certain metamagics. Spirits with these powers can tach the coresponding metamagics. Any spirit that has possession can teach it as a metamagic, for example. Likewise, some spirits know certain things due to their nature but can't put them to use. Most spirits can teach invoking but no known spirit (except, perhaps, an insect mother) can use it.

What advantages do great forms get? Can any force spirit be a great form? And is it supposed to be harder to summon them?

It's harder, and the drain is a lot nastier.

For one thing, they usually get more powers. Example: spirits of man get the divination metamagic. and so, a GF SoM can teach an initiate divination.

Also, they get armor and reach bonuses. If you're using 3rd ed rules at least, (IIRC) every two grade levels you can add a point of armor. A point of reach for every 4 (more or less).

Also, some attacks get better. A GF earth elemental can engulf multiple opponents for example. They're cool.

So under SR4 rules, binding great forms = death.

Theoretically, a metahuman magician could learn metamagics from unusual spirits like Baba Yagas, Jack Frosts, Shedim, Faeries, Men-of-the-Woods or other spiritual entities that possessed the correct powers.

Or, maybe we could have lots of foci and absorb all the drain that way. A power focus to dwarf the spirit's dice pool and an approrpriate binding focus to absorb the drain.