Actually, it is pretty easy to play by posts. In fact, it is easier to describe stuff in a post then in real life. As for the battle grid and minis, it is not hard either. You can simply make a picture, or use some excel grinds instead.
Here is some examples:A battle map from one of the D&D game I am in!
This is an example post of battle (4e)![example]
Bebop raises his songblade up with jubilance and it hums slightly in response to the lightning filling the chamber. The gnome's eyes sparkle as he levels the blade once more at the gelatinous blob. "Our passage here is overdue! You shall soon be naught but goo!"Actions:Standard-
once again with the old Vicious Mockery
, 17 vs Will for 12 damage and the cube takes -2 to attacks until the end of my next turn.[/example]
After that, the DM reduces the HP of the Gelatinous Cube and make a note that the cube has -2 penalty to attack rolls, if Bebop's attack hits.
For some 3.5e examples, just go here