Spell Completion
Scrolls—there are several references to the spell on a scroll being cast once the scroll is activated:
If she meets all three requirements but her own caster level is lower than the scroll spell’s caster level, then she has to make a caster level check (DC = scroll’s caster level + 1) to cast the spell successfully.
A spell successfully activated from a scroll works exactly like a spell prepared and cast the normal way.
However, these do fall somewhat short of saying that spells are always cast from scrolls; much of the description uses activated as the verb instead. Super-strictly speaking, one could argue that if you don’t need the caster level check, you aren’t casting, and then even though the spell “works exactly like a spell prepared and cast the normal way,” that says nothing about you. Unlikely to fly with many DMs though.
Minor Schemas—from Magic of Eberron, these stone tablets are in many ways just reusable scrolls, but there are a number of important differences. One of those is that it makes no mention of the spell in the schema being cast (though it does say that it is “much like a scroll,” which is thoroughly unhelpful).
Spell Trigger
Wands—quite clearly state that the spell in the wand is being cast when the wand is activated:
Wands use the spell trigger activation method, so casting a spell from a wand is usually a standard action that doesn’t provoke attacks of opportunity.
Scepters—from Lost Empires of Faerûn, these items are basically wands that can go up to 7th-level spells, and that includes copying the wand blurb about casting upon activation:
Scepters use the spell trigger activation method, so casting a spell from a scepter is usually a standard action that does not provoke attacks of opportunity.
Staves—once again, identical to wands and scepters:
Staffs use the spell trigger activation method, so casting a spell from a staff is usually a standard action that doesn’t provoke attacks of opportunity.
Command Word
Some items of this sort, like the boots of teleport, have the user cast a spell when activated:
exactly as if he had cast
Most, however, do not say any such thing, and the command word rules in general do not mention casting. So command word rules should be safe.
Use-Activated
I don’t know if spell-storing weapons would be considered “use activated” (certainly no mention of a command word is given), but those mention casting. None of the others in core, anyway, do, but be sure to check the full descriptions of any items you’re looking to use.
So in conclusion: spell trigger items are definitely out, scrolls are probably out, and minor schemas are definitely OK. Command word and use activated items are usually fine, but you’ll need to double-check individual item descriptions to be sure.
Finally, please do note that skill tricks can only be used once per encounter. Swift Concentration therefore can only be used once, that is, in one round you can concentrate as a swift action. Centering a build around this seems... very difficult. You might have more like with a similar idea using psionics, with the solicit psicrystal power. With that, you won’t even need to worry about any of the above, since the psicrystal is concentrating, not you.
