iPhone owners have been waiting for what seems like an eternity for 2D Boy’s World of Goo to appear on their handhelds.

In reality, 18 months have passed since the famed indie developers first mooted that a World of Goo iPhone edition was in the works.

Of course, the iPhone’s big brother iPad launched in the meantime, and 2D Boy switched their attention to readying the physics-based puzzler for the larger touchscreen. The net result was - in the developer’s own words - the best version “by far” of the bridge building extravaganza.

All of that patience on the part of iPhoners is about to be rewarded, though, as 2D Boy has finally submitted the iPhone strain of World of Goo to Apple’s approval team.

In a move designed to offset some of the anger expressed by early adopters of World of Goo HD who saw the price drop dramatically soon after release, 2D Boy will run an opening day promotion:

We realized after the fact that the way we set pricing for the iPad version wasn’t very friendly to fans and early adopters (started at $10, lowered to $5 after a month when we realized $10 was too high). Having learned some lessons from our first App Store release, we decided to do things in the most transparent and fan-friendly way possible this time around.

The iPhone version of World of Goo will be priced at $2.99 in the US (and the usual equivalents elsewhere). BUT, it’s going to be discounted to $0.99 for the first 24 hours after release as a way to say thank you to the early adopters.

Additionally, we thought the most fan-friendly thing to do with the iPad (HD) version is to make it universal. So if you already bought the iPad version, you will essentially be getting the iPhone version for free. Bon appetit!

World of Goo on iPhone should be out “soonish”, but please note it’ll only run on iPhone 3GSs and iPhone 4s.