Actually, there were two for the GBA and two for the DS
http://en.wikipedia....ki/Advance_Wars
http://en.wikipedia....ack_Hole_Rising
http://en.wikipedia....rs:_Dual_Strike
http://en.wikipedia....s:_Days_of_Ruin
Since the Advance Wars series' has only been on handhelds, I'd imagine that the next installment would be on the 3DS.
If they make Advance Wars 3DS (and make it a successor to Black Hole Rising or Dual Strike rather than the disappointing Days of Ruin), I may be tempted to buy a 3DS