BattleTac

Yeah, that's a phone mounted to an airsoft gun, with a HUD. You want it.

BattleTac is the manufacturer of a program specifically designed for milsim paintball and airsoft games, which provides you with a Future Warrior-esque tool set.

Here's the company's description: 

"BattleTac provides real-time GPS tracking, instant messaging and navigation on the battlefield. Using BattleTac you will always know where your comrades are on the battlefield and what they are doing. So BattleTac gives you essential information to make better tactical decisions and to be victorious.

Features

Live GPS tracking of combat units
Target command delivery - you can easily send commands to your units like "go to that location" or "go and meet unit Whiskey"
Battlefield navigation - if you have a target, the system helps you hit it
Instant messaging, textual command and report delivery - you can send out texts like "attack in 30 s" or "see 3 enemy 100 m N"
Technology

The BattleTac system uses internet technologies, so to use it, you need to have mobile internet access. Note that this is not a technical issue, every modern mobile phone can access the internet. The system runs on your mobile and communicates with other units over the internet.

To track your position, you need a GPS receiver. If your phone has one built-in, you are lucky. If not, you can buy an external Bluetooth GPS receiver for USD 50 or so."

I tried, briefly, to download and Battletac, but I got a bit confused with the installation instructions, hopefully someone else will have more luck. If you do get it up and running, send me a pic of you using it!

Props to JC for sending me the info on this.
BattleTac's Website