Then it would seem a swordmage using a wizard power with implement keyword could use his sword, since they are both arcane powers. A wizard would use a wand/orb/staff, a swordmage uses his sword.
Tellerve
No it wouldn't. The Implement use class features all clearly and specifically say "A [CLASS X] wielding a [IMPLEMENT TYPE Y] can add its enhancement bonus to the attack rolls and the damage rolls of [CLASS X] powers, as well as [CLASS X] paragon path powers, that have the implement keyword."
Implements themselves are not broken up by the classes that can use them, the classes are broken up by what implements they can use. A multiclass wizard/warlock can use a single wand for all of his powers, because both classes say you can use a wand with that class's powers, and there's no such thing as a "warlock wand" and a "wizard wand." That same character
cannot, however, use a rod with his wizard powers, because the use of a rod is a warlock-specific ability that only works with warlock powers. It's the same with swordmage/wizard. Swordmage says "you can use a sword with
swordmage powers," wizard says "you can use a wand, orb, or staff with
wizard powers." There is no ability that allows you to use the implements unique to one class with the powers of another.