JackTheRipper has a wide selection (over 40 of them) of farts to choose from ranging from the "Buggle Boy" to the "Rrrip Roaring". The 99 cent application also has a Sneak Attack Mode where you can use a timer to unleash the room clearing sound effects and Security Mode that lets one rip if someone picks up your phone.
The app includes two games, Fart-a-Piano and Fartman Says (akin to Simon Says) to keep things lively. In trying out JackTheRipper it was a very stable application. Some of the sound effects are hard to sell as the real thing while some are rather convincing. PSA: Don't test out this app in a crowded restaurant with your wife holding sharp utensils.
No telling if Windows Mobile has risen to the occasion with the release of JackTheRipper but the app is well suited for the jokester in all of us.