Good mobile strategy games.

you filthy casual

Age of Conquest? It's like Risk. You gotta pay for it though...

I don't think such things exist

Disgaea, Joan of Arcadia, FF: Tactics. Advance Wars series.

A grand strategy game on a mobile device? Isn't that an oxymoron?

Freeciv on Android if you want a turn based strategy game? Its essentially Sid Meiers Civ on mobile so there isn't much of a storyand the UI takes a bit of getting used to but it's not 'bad' for a mobile TBS in my mind

StrategyHub.com...

For DS/3DS I can recommend the Fire Emblem series (there are two (in the west) for GBA, so if you have an old DS, I can recommend those as well).

For android, I can recommend Call of Cthulhu: Wasted Land.

None of those are grand strategy, but they are good.

Android:
Dungeon Ascendance
Star Traders RPG (maybe not very strategic but you might like it )

Civilization Revolution?If it is on Android.

The DS (and by extension the 3DS) has tons of decent-to-great turn-based strategy games. Advance Wars, Disgaea (not a fan of that one myself but lots of people love it), Fire Emblem, Final Fantasy Tactics, Pokemon Conquest, Drone Tactics, Valkyrie Profile, Front Mission, Devil Survivor (if you don't get the new and much improved 3DS versions) and many more are all worth a shot. And since they're DS games, you can play them on your 3DS without region restrictions.

For the 3DS, I recommend Ghost Recon: Shadow Wars, Fire Emblem: Awakening, Devil Survivor: Overclocked (an updated version of the DS Devil Survivor game with added story, new demons, full voice acting, etc.) and maybe Project X Zone. That last one isn't that great as a strategy game (it's shallow and too easy, with the only challenge being that you get to fight TONS of enemies on the later levels), but it's a good fanservice crossover with lots of cool characters and a good sense of humor.