Gmail's new Inbox app is pretty awesome, but it's still invite-only. If you have a friend that's using inbox, you can get access on your own device with their help—even if they don't have any invites to give out. The process, courtesy of WonderHowTo, is simple: Download Inbox on your phone through its app store, either Android or iOS. You won't be able to sign in with your account, since you don't