Open Feint, Plus+ Network, Crystal, Scoreloop, Gameloft Live, Agon Online - the gaming network wars are in full swing on iPhone and right in the thick of the fray are achievements.

Whatever you call them - achievements, awards, points, or trophies - they're quickly becoming an important part of the iPhone gaming experience.

Dozens of games integrated with these networks support achievements, yet few do so to great effect.

Annoying hidden achievements, scrooge-like low point awards, and trophies that demand more than a fair share of time make unlocking achievements in some games a laborious prospect.

There's a way to incorporate achievements without frustration, while at the same time demanding skill and time.

Challenging is the keyword here. Following these five principles ensures challenging achievements without aggravation.

1. Don't skimp on points!

It should go without saying that the right balance of points for difficult achievements versus easier ones is critical to keeping you playing a game even after you've completed it. Unfortunately, too many games toy with point totals that sour any desire to go back and play.

Nothing is more frustrating than spending hours completing a lengthy adventure to only receive a paltry points reward . Finger Physics is hallmark offender, dishing out a pathetic 10 point award for completing all of its 72 levels. The same number of points are awarded for finishing all of the Egg levels in the game, which is only a fraction of the total. In this case, the completion achievement should be significantly larger.

By far the worst game has to be Eleminis with its cruel set of 1 point achievements. The entire game nets you a stupidly low 30 points, which you can get within seconds of starting up some overly generous titles.

Macabre fairy tale Red Rage comes in close second with a single 10 point achievement. Thanks, guys.

2. Don't award too many points!

The problem isn't just skimping on points, as many titles award too many points for easy acts. Boppler doles a whopping 100 points for racking up a small 30,000 score that takes just a moment to earn. Fame grants an easy 50 for simply playing as both its male and female characters.

As great as it is to quickly rack up points with these games, it feels cheap.

Reconfiguring the point totals so that easier achievements have lower values and harder ones net swaths of points would actually make earning points a reward instead of a gift with purchase.

Lastly, consistency with other games is critical. Eleminis's low 30 point total makes it unattractive in comparison to the 1,000 available in Fame.

When considering achievements alone, you're more likely to play a game with a higher point total. As such, matching the overall point total of other games ensures a level playing field.

3. Limit multiplayer achievements

Multiplayer achievements are without question the greatest source of aggravation when it comes to achievements. Fortunately, there aren't many such games to be found for iPhone and iPod touch yet, but it's an important point to highlight.

Games that focus solely on multiplayer like Eliminate are exempt from this rule as there's not disconnect between single and multiplayer. But, in such cases, it's important that achievements are not unduly weighted toward chance.

Having specifically asked producer Chris Plummer about Plus+ awards in Eliminate, he assured us that the balance of points was something of which ngmoco was mindful. He did admit that there are a few awards that require reaching the highest levels of the game, but the vast majority can be earned without investing 100 hours of your life.

For games that don't focus on multiplayer and include a single player component, it's a good idea to focus on single player achievements. Designing multiplayer achievements is tricky, so it's best to avoid them altogether.

Awards for completing a multiplayer match or reaching an experience level online are fine, but ridiculous achievements such as requiring a dozen head shots in a single two minute round is not kosher.
Word Fu, which recently added Plus+ awards, does a great job of this by including a single award for winning a versus match. The rest are all skill-based awards for the single player game.

4. Reward completion of single player story/campaign modes

An extension of the previous point, it's a good idea to reward completion of a single player story mode or campaign. This is a fantastic way of encouraging a run through the game. Spreading several achievements or awards through the course of the campaign is recommended as a way of creating a sense of reward the whole way through.
Darkest Fear does an excellent job of this, awarding achievements for completing levels throughout its short story mode. Above & Beyond Air Combat also succeeds in this, delivering achievements at specific points in Conquest mode that give you a feeling of accomplishment. Of course, Rolando 2 is a great example as well with its well-spaced awards.

And all three games give a heap of points upon finishing their respective single player modes and they are the examples to follow for how to design good achievements.

5. Make all achievements not tied to plot spoilers viewable

There's no reason to hide achievements if they aren't tied to plot spoilers. Unify, for example, does a disservice by keeping its achievements secret, preventing you from knowing what exactly needs to be accomplished to earn them.

Hiding achievements doesn't make them more challenging to earn, just harder - like fumbling in the dark for a light switch.

Divulging the conditions for achievements not related to the story actually encourages playing to unlock said achievements. When you know what you're working toward, there's more motivation to keep playing or come back to unlock achievements after you've finished the main game.

After all, who can argue against more reasons to play?