(Wired) -- A year after its release, Google's open source Android operating system has become a sensation.





After a slow start, it is now available on at least 12 phones, with more devices waiting in the wings.





Good news for Android fans, right? Not really, say some developers.





A slew of problems have made managing Android apps a "nightmare," they say, including three versions of the OS (Android 1.5, 1.6 and 2.0), custom firmware on many phones, and hardware differences between different models.





For users, it means apps in the store could be buggy, might not work well depending on their handsets, and could deliver a frustrating experience.





Unaware of the increasing back-end complexity, they would then be more likely to leave bad reviews for those apps -- a potentially lethal blow for small businesses, say developers.





"Instead of working on updates to our apps, we find we are trying to make each app work for multiple versions of the OS and different hardware capabilities," says Chris Fagan, co-founder at Froogloid, an Android-focused application development company. "We are not complaining about all the growth, but if you are a small or a new Android developer coming in and trying to learn I could see your head exploding. It would be overwhelming," he says.





The problem echoes similar concerns over Java in the 1990s. Originally touted as a way for developers to build apps that would run on any computer ("write once, run anywhere"), developers found that wide variations in Java virtual machines as well as available hardware meant that Java's promise was really "write once, debug everywhere."





While Java is still used -- particularly in the mobile space, where it powers games and other apps written for Java-capable cellphones -- it is not nearly the cross-platform panacea it was originally conceived as.





Fagan's concern about the fragmentation of Android is being echoed by other developers, says Sean Galligan, vice president of business development at Flurry, an mobile app analytics company.





"There's no question that we are starting to hear developers express concern," says Galligan. "Android is growing very fast and there's a lot of excitement for it but it's also a lot for work, especially for medium and small developers."





Since the launch of the first HTC T-Mobile G1 phone running Android OS, a number of handset makers have jumped on the bandwagon. HTC alone has five Android handsets available, while others like Motorola have shifted completely to the Android platform.





In the past two months, Motorola released two new Android-based handsets, the Cliq and Droid. And in a bid to differentiate themselves, handset makers are creating custom user interfaces like the HTC Sense, the Motorola Blur and the Rachael UI from Sony Ericsson.





Android phones vary significantly in the hardware, too -- phones with and without camera flash, some have physical keyboards, others don't.





"You may build an app that works perfectly with all three firmwares, but then when you run it on carriers' ROMs it completely blows up," says Fagan. "So we find ourselves having to create apps that are compatible with multiple firmwares, multiple ROMs and multiple devices with different hardware."





It's in sharp contrast to the iPhone platform.





Apple has tightly controlled the introduction of new iPhones and updates to its operating system. It has just three iPhone models available since it first introduced the phone in 2007. And all iPhone users are prompted to update their phones to be on the same version of the operating system.





While Apple pioneered the app store idea with the iPhone, Android, too, offers Market, a store for distribution of third-party programs. Unlike with the Apple app store, Android developers do not have to go through an approval process to get their apps on the Android Market.





Currently, the Android market has about 10,000 apps compared to the 100,000 in Apple's app store.





For developers, Apple's autocratic ways may be
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