Theres a couple OM codes that craneballs let out on there FB page. Just to save you some time searching, the codes are:
xmas (30 free OM)
craneballs (30 free OM)
Also, save your OM, and get the first sniper rifle available (cant remember the name of it atm... but its good... its the bolt-action one...)
If youre willing to save your OM for a bit, wait until you have enough for the other sniper rifle (havent tested it out personally, but it looks like it could be good)
tags: cheats, codes, tips, iphone 4, review, not working, guide, hacks, add friends, grenade, launcher, upside down