For Adobe, the rise of mobile, and the iPhone and iPad in particular, has been bittersweet.

Yes, the company most recognizable to consumers for its Reader and Flash products, has plenty of new opportunities thanks to mobile, but exploiting them has required the company to look at a number of Plan Bs.

The primary reason: Apple doesn’t like Flash. Adobe tried to persuade Apple that Flash isn’t so bad, but that wasn’t going anywhere, so the company has been increasingly betting its mobile future on other technologies, like HTML5.

Adobe’s investment in HTML5 continued yesterday when the company announced that it was buying Nitobi, the creator of the PhoneGap mobile development framework.

PhoneGap enables the development of mobile applications across multiple mobile platforms, including iOS and Android, using HTML and JavaScript.

Through PhoneGap, developers can access native functionality, including the accelerometer and filesystem, and then build their PhoneGap creations as native apps that can be submitted to marketplaces such as the App Store and Android Market.

Concurrent with the Adobe acquisition, Nitobi announced that it is donating the PhoneGap code to the Apache Software Foundation, meaning PhoneGap will remain freely available as an open source product.

Adobe will operate PhoneGap Build, a hosted service that allows PhoneGap users to upload their PhoneGap projects and automatically have them built into apps ready for submission to the various app stores.

On the surface, the acquisition makes sense. Adobe has seen the writing on the wall vis-à-vis Flash’s role in the mobile ecosystem, and is shifting its mobile investments to technologies like HTML, JavaScript and CSS — technologies that obviously have a place in quite a few Adobe products, and which many of its customers use regularly.

But digging a little deeper, it’s not clear that Adobe is getting something it can work with long-term. PhoneGap is essentially a tool for ‘wrapping‘ an application built with HTML, JavaScript and CSS into a native app.

In effect, the app is a web browser running a web application on the phone. PhoneGap’s APIs allow access to some native functionality, but PhoneGap doesn’t really create a native app.

In some cases, this is quite satisfactory. But the question for Adobe is how big the market will be for this type of solution in a year or two.

At one end of the spectrum, you have cross-platform mobile development products like Corona and Appcelerator, which produce truly native apps. On the other, you have solutions like jQuery Mobile and Sensa Touch, which help developers create better browser-based mobile web experiences.

And, of course, efforts are under way to make hardware-level functionality more greatly available to mobile web apps, meaning you increasingly won’t need solutions to bridge the gap between the hardware and your web apps.

It’s unclear where PhoneGap and Adobe fit in this landscape. Other tools create true native experiences, while the mobile web itself is getting more and more capable.

Adobe may find that there’s a market for a tool that wraps the mobile web in a native app, but that market may not exist for very long as the sophistication of native apps and the mobile web demands more of developers.