I like the one-time-IAP model.

You can either make some of your game (a few levels, a fraction of the overall length) free then charge for the rest. This gives me a chance to play your game, and if I like it I'll pay.

You could also add a one-time-IAP which subtly improves gameplay. Most do this as a "buy to remove ads" but the Piggy Bank in Crossy Road is a good example of a clever use of this model.

When the Honest Android Games blog was going, it would cover games with fair one-time-IAP to unlock full games, so don't feel like you're selling out because you include one purchase. After all, this was the shareware model in the 90s and that was more than fair.

Interestingly, that model is essentially the "shareware" model that games like DOOM originally used, except that the way the game is distributed (previously retailers, now app stores & IAP) has changed.

There are all sorts of business models that work for cell phone games. Here are the three most common:

* Freemium - Get users then try to charge them money later

* Up front - Get paid by people, then provide them with a game

* Ad-based - Get users and then sell their attention to companies

The reason why freemium is so popular is that it makes sales much easier. Users can try a game with zero risk of spending money on something they don't like. For this reason users are more likely to download your game instead of a paid app. Once they get hooked, they are more likely to spend money. I would argue this is a good thing for users and for publishers. Users have reduced risk and publishers can get in front of more potential customers.

Fremium doesn't have to be pay-to-win or scammy. Depending upon your game, you can sell access to more levels, better AI, multiplayer support, new graphic tiles or other items that provide real value without being scammy. The original Doom worked like this... The first levels were free, but if you wanted to play the entire game, you had to pay up. The fact that the first part was free allowed it to spread like a virus and boosted its sales immeasurably.

Freemium can be applied to almost anything. I wrote a book and give away one chapter. Want the rest? Time to break open that wallet. It doesn't feel scammy at all. Folks can read the free chapter and get a feel for the type of content and quality that the rest of the book contains. Less risk for them, more money for me.

Freemium certainly seems to be a very successful model, but that doesn't have to mean other models are obsolete. Important to keep in mind, though, is that on mobile app stores, there's a ridiculous number of games available, and many of them are free. You need to have a plan on how to compete with free.

There different ways to handle free or freemium:

* a playable demo (limited in features or scope, like only a few levels) with a paid full version - this is the classic model, and it's a really good and honest one. The full version could be either a separate app, or unlockable in-game (through in-app purchase or entering a code).

* a full featured, ad-loaded free version and an ad-free paid version. Popular on mobile because ads are easy to do. People who don't mind the ads might never move to full, but ads can apparently bring in a lot of money. You could even do just the ad version, but some people hate them and don't mind paying for an ad-free version if they like the game.

* a limited, ad-loaded demo version. This one is a bit two-faced and feels a bit more sleazy to me; it's simultaneously a limited demo from which you hope people will upgrade to full, but you also want ad revenue from the demo, which itself is basically an ad for the full version.

* a free limited version with multiple, staged upgrades to more versions. Sleazy if you're dishonest about this up-front; it's a bait-and-switch if they expect to buy the full version and then don't get it. But if you're open about it, buying access to more levels or more worlds could be a totally reasonable way to do this.

* a free full version with in-app purchases that give in-game bonuses. This is the big one that seems to be incredibly effective (Clash of Clans, Candy Crush, Hay Day and all those other mobile games use this). Most people will just play for free, but a small group of addicts, or "whales" will be paying through to nose to fuel their addiction to your game. Ethically creepy if you really want to milk the addiction angle.

I'm sure there are other variations that I'm forgetting at the moment.

Why iOS only? Pay to play model still works pretty well on PC. See the numbers for yourself:

* http://steamspy.com/

* http://steamspy.com/genre/Indie

How about free one level, $1 to enable rest?

Not scummy but also gives people a free trial.

There is another model, though I'm not sure it works for IOS. The Subscription model. You get access to the full game as long as you continue to pay for it.