Tongues have been set wagging in technology circles by Adobe chief executive officer Shantanu Narayen's recent statement that Adobe Systems is working toward getting its ubiquitous Flash technology onto the Apple iPhone.

However, in an interview to Bloomberg Television on the sidelines of the World Economic Forum at Davos, Narayen acknowledged that even after months of striving, a workable version of Flash for the iPhone is proving a tough nut to crack.

"It's a hard technical challenge, and that's part of the reason Apple and Adobe are collaborating," Narayen said. "The ball is in our court. The onus is on us to deliver."

But experts question exactly how much the two companies are willing to collaborate. Back in may last year, Adobe had said, "To bring the full capabilities of Flash to the iPhone Web-browsing experience, we do need to work with Apple beyond and above what is available through the SDK (the iPhone software development kit) and the current license around it."

This brings into focus a key issue: however far along Adobe actually is with reconfiguring Flash for the iPhone, it will need a definitive thumbs-up from Apple to bring the technology to the public. Narayen's "collaborating" could mean that Apple is giving Adobe access to the iPhone that other companies cannot get from the iPhone App Store. This would be essential if Flash were to work as a plugin, the way it does on the Mac.

Apple hasn't opened its browser up to anyone yet. It makes some sense for it to allow Adobe in if Flash ran well enough - because many Websites still rely on Flash for content and navigation. And some some competing phones, including Palm's forthcoming Pre, do offer Flash. But there's no guarantee it will run well enough on the iPhone to watch streaming video, for instance.

Or, as John Gruber writes in Daring Fireball, "Another way to read it is that 'collaborating', without any details of what that collaboration entails, is just an empty word that could mean anything." Because even if Adobe does an excellent job porting Flash to the iPhone, it still needs a buy-in from Apple, which has little incentive to make an exception for Adobe that might antagonise its other customers.

In early March last year, Apple chief executive officer Steve Jobs had thrown cold water on hopes for a Flash-iPhone coexistence, saying the PC version of Flash "performs too slow to be useful" on the iPhone, while the Flash Lite version for mobile phones "is not capable of being used with the Web".

In a presentation in November, Adobe chief technology officer Kevin Lynch had said, "We are in the midst of evolving Flash Player 10 for mobile. We're taking the full Flash Player and making that run on the higher end of the mobile market." But the iPhone was conspicuously absent from the presentation.

So will America's most popular hand-held device finally become Flash-enabled? It is hard to tell until there's either a Flash app for the iPhone or more definitive comments from either company.