Revert has a number of meanings, most of which relate to the notion of returning to a previous state. You can't employ it to mean "reply" in a revolting phrase like "we will revert to you". It's simply not on.
Letter picture from Shutterstock
I'd never actually encountered this ghastly expression until it showed up in a message sent to my brother Alex during his stint as guest editor on our sibling site Kotaku this week:
Your email has been forwarded to the concerned department and we will revert to you shortly.
The first error in this sentence is 'concerned department'. What the sender presumably meant was 'department concerned', though it would be better to avoid any ambiguity or confusion by writing 'relevant department'.
The other problem is 'we will revert to you'. 'Revert' does not mean 'reply'. At first I thought this was simple pig ignorance, a frequent factor in poor writing. However, a little digging around suggests that this a quite common usage in US English. However, it doesn't even rate a subsidiary mention in the Macquarie Dictionary, which remains our oracle for these matters.
This is yet another example of where Australian and US English differ in what counts as correct. If Americans must use "we will revert to you", they can. But it has no place in professional communication or formal writing in Australia (and it's not a phrase you'd need to use casually).
Lifehacker's Mind Your Language column offers bossy advice on improving your writing.