"... Unlike the three Nokia Internet tablets preceding it, the Nokia N900 is the first Maemo device to include phone functionality ..."

"...The N900 functions as a mobile Internet device, and includes e-mail, web browsing and access to online services, a 5-megapixel digital camera for still or video photography, a portable media player for music and video, calculator, games console and word processor, SMS, as well as mobile telephony using either a mobile network or VoIP via Internet (mobile or Wi-Fi).[7] Maemo provides an X-terminal interface for interacting with the core operating system..."

"...Maemo 5 is Nokia's adaptation of the Linux desktop environment for a pocket-sized device..."

Amoungst other os's ..."An application called "Easy Debian" installs a Debian LXDE image on the internal memory, this facilitates the running of applications within Maemo such as IceWeasel (Firefox browser) and all of the OpenOffice.org suite. Within the LXDE interface, other applications in the Synaptic package manager that are included in the Debian installation, such as GIMP, can be run. Software can also be added to Debian using a chroot tool within Maemo using Synaptic or apt-get at the command line, such as Stellarium or the zim desktop wiki, and this can then be accessed either via the LXDE desktop, by icons in the program manager or shortcuts on the desktop. This has even been used to install the Hercules Mainframe emulator to run MVS 3.8J on the phone...."

In short it is an MID...specifically a NIT(technically 5th official release in device line if you count The N810 wimax as the 4th)... it isn't semantics...it is the family of the device line.
with phone functionality... so it's also a phone.
with the ability to run alternate pc operating system environments, desktops and programs... so it's also a pc.

in REAL short I'd call that a convergent device.