There have been a couple of form factors in recent years that have completely failed to capture the public's imagination, despite their promising capabilities: Tablets and Mobile Internet Devices (MIDs).

However, with the dramatic level of rumor circulating about Steve Jobs and Apple's pet tablet project, there may be hope for that form factor after all. And with Nokia's announcement of the N900 today, the MID concept looks like it might stick around too.

But it may not gain traction, so much as evolve into a new high-powered mobile phone category, akin to a "smartbook," but minus the bookishness.

Nokia has been making MIDs for about four years, and the N900 will be the successor to the N810. However, it will be radically different from its predecessors, if only by the simple fact that it now contains quad-band GSM and HSPA cellular radios and can be used as a phone.

With the N900, Nokia has resolved some the issues which prevented MIDs from breaking through. First, MIDs were typically built to be Wi-Fi devices, anchoring them down to hotspot and home use. Not really as mobile as the name "Mobile Internet Device" would suggest. Nokia attempted to beef up the mobility of the form factor by aligning with WiMAX, but with dissolving interest in the wireless standard, the company said it was bringing 3G to its tablets in late 2008. And then reportedly sacked the WiMAX effort at the beginning of 2009. By equipping the device with cellular and mobile broadband signals in addition to Wi-Fi, it has finally become a mobile form factor. The addition of cellular connectivity also plays into the price, which I'll talk about later.

Secondly, MIDs are awkwardly fashioned in between standard form factor sizes. They're too big to fit in your pocket, and too small to view at laptop distance. You'd have to hold them as close as you would a phone, but without any of the ergonomics of a phone. Nokia solved this by keeping the resolution up (800 x 400) and shrinking the screen down to 3.5 inches, the now-standard touchphone screen size.

Thirdly, MIDs were priced out of the range of mobile phones and in the range of notebooks, despite not being as powerful. It is actually the same issue which doomed the Foleo to failure yet made the Eee a triumph. The price to power ratio was just uneven for MIDs. This has not exactly been resolved yet. The N900 is expected to sell for $711, yet it only carries a 600 MHz processor, 256 MB RAM and 32 GB of storage.

However, since it's a full-fledged cellular device, it will likely be subsidized through national wireless carriers and brought down into the smartphone price range.

Even the chipset treads the fine line between MID and Smartphone. The TI OMAP 3430 is described by Texas Instruments as supporting "all levels of handsets, from the entry-level multimedia-enabled handsets to high-end Mobile Internet Devices (MIDs)."

Adding to the categorical confusion is Maemo, Nokia's Linux-based tablet OS which the N900 runs. Anssi Vanjoki, Executive Vice President of Markets at Nokia said, "The Nokia N900 shows where we are going with Maemo and we'll continue to work with the community to push the software forward. What we have with Maemo is something that is fusing the power of the computer, the Internet, and the mobile phone, and it is great to see that it is evolving in exciting ways."

So it's got the chassis and connectivity of a smartphone, and the guts and operating system of a MID. It looks like Nokia has either rejuvenated the MID, or created a new mutant.