That's right, there is no grid in my sandbox styled campaign, at least not how one is used in 3.5 and especially 4e D&D.
There is a reason Adventure Paths are popular with the 4e crowd (and started with the 3x crowd)- the adventures usually come with battle maps or tiles.
3.5e is nearly impossible to play with out a grid, and the amount of house ruling it would take to remove the grid from 4e would make it a totally different game (5e perhaps?).
It's hard to run a gridded game with a sandbox. Sure, you can use a battle mat and write it in washable marker, or maybe pull a map from your collection that you've used before that kinda fits the location, but it's not a great solution. Heck, you could map out battle maps for all of your possible random encounters, but then when would you have time to game?
Did anyone use a grid with G1-3? T1-4 (TOEE). None that I know did more than a sketch and a room description
That is why sandbox style play is very much "Old School", where counting hexes and spell templates are replaced by a quick description or sketch and the Theatre of the Mind.
Not that I have a total aversion to using a battle mat / map if it helps sort things out. I just don't want my players, my campaign, or myself being a slave to it.
The moment players start counting, measuring, checking facing or asking about spell area effect templates I know the map has gone from imagery to grid.
There is no room for a grid in my sandbox, but a map, mat, whiteboard and the like are welcome. Even if it has little hexes or squares on it. Just don't treat it as a grid.