According to Harald Welte's Anatomy of contemporary GSM cellphone hardware (2010), "A smartphone is a phone that has a dedicated processor for the GSM protocol stack, and another (potentially multi-core) general purpose processor for the user interface and applications." and "A feature phone is a phone that runs the GSM protocol stack (the software implementing the GSM protocol)as well as the user interface and all applications on a single processor."
The Replicant wiki has a lot of information on various Android and GNU/Linux smartphones.
That wiki also have information on many devices that the Replicant project doesn't want to support as it is still relevant to free software support (or the lack thereof) for smartphones and tablets.
For feature phones, the osmocomBB wiki has a lot of information on various devices that are supported or could be supported by osmocomBB and other related projects (Nuttx, etc).
However some devices do not fit in either categories:
- There are some smartphones without any touchscreen that have a feature-phone like formfactor. Due to the limited input capabilities (feature-phone like numpad) they are not well suited to run common Android or GNU/Linux desktop environments. As some run derivative of FirefoxOS, it would still be interesting to do some research on them, for instance to get the corresponding source code.