Good to hear someone's at least considering it. Here is another link with some info...
http://www.6mmbr.com/index.html
is a website focused on shooters that shoot long range and are after the very last bit of accuracy. It is nothing to drop thousands into a rifle for the slightest edge. I'm not sure how many own an iPhone or ipod Touch but I'm sure money could be made. If you look at the Horus Vision site you can see where their software sells for hundreds and they even offer it preinstalled on a PDA, so there is a market.
Of course the cheaper the App would be the better it would sell, maybe consider a "lite" version.
If you are really serious and would like to see what could be possible on the LEO/Govt side try a serious forum like
http://www.10-8forums.com/ubbthreads/ubbthreads.php
They have people that post there who are responsible for dept. and agency procurement.
On the ballistics page of the 6mmbr.com
http://www.6mmbr.com/ballistics.html
There are links to some free ballistics programs and a free spreadsheet could give you an idea of what kind of calculations you would be looking at.
Poke around and I think you might see an oppertunity, you have at least 2 sales here
Lord knows we don't need another flashlight.
A few other forums to guage interest....
http://www.m4carbine.net/
http://www.thehighroad.org/
http://glocktalk.com/forums/
Also note, I probably don't have to tell you, that shooting forums are like all forums be careful how you post, so it doesn't look like spam.