“But am I going to have to jailbreak my device?” - Not necessarily. Maybe you snagged the iDOS app when it was briefly sold in the iTunes store. Even those with weak google-fu can probably locate an .ipa download of version 1.0 fairly easily (iDOS 2 was free while still available). If you’ve jailbroken, you’re on your own - look for DOSPAD in Cydia.
Once you have iDOS installed, download and install iPhone Explorer. It’s free and works with both Windows and OS X.
Now let’s grab the abandonware MegaTraveller and its manual. Unpack the MegaTraveller files into a folder with a short name.
Mount your iOS device as a hard drive with iPhone Explorer and navigate to Apps/iDOS/Documents and drag your folder with all the Traveller game files into it.
Disconnect the device and launch iDOS. Click on the C: sticky note icon at the bottom of the screen. You’ll be dropped to a command prompt in DOS. Now touch the top of the keyboard icon at the bottom of the screen to bring up your keyboard. Type “CD X” where X is the name of your Traveller folder. Mine is Trav. Then type “trav” to start the game.
Once you’ve selected the screen and sound drivers (anything should work) you’ll be asked to enter a question using the rules book. An example is “Please refer to page 56 in the manual. How much cargo can a Small Interplanetary craft carry? A. 2 B. 8 C. 20 D. 12” Ah the olden days, before DRM... Just open up the manual you downloaded earlier in a word processor and do a search to find the answer.
Voila, that’s it! You can hide the keyboard again when you need to by clicking on the gear symbol in the middle left of the screen. Does it suck? Of course! Especially on the iPod Touch or an iPhone. Magnified on an iPad though, it’s probably not too bad - certainly playable on a transoceanic flight. There’s always MegaTraveller 2, too.
If you just want to play it in your browser, don't bother reading how to do this on the site where you can download the DOS files - go here instead (this won't work in iOS, but it might on your Android). You’ll still need the manual to start the game though.