Below you'll find a list of the currently available native pure-Linux (non-Android) mobile devices

Smartphones and tablet PCs

Librem 5 [$$$]

Arguably the first modern Linux smartphone.

Released: September 2019
Price: $650/$700
Specs: i.MX8 SoC (4xA53), 3/32GB, 4G modem, 3500mAh battery
OS: PureOS, postmarketOS

Necunos [$$$$]

Technically not a phone, as it contains no modem; rather a PDA. Made in Finland

Released: ?
Price: $1360/€1200
Specs: ?
OS: Debian, postmarketOS, Maemo, Nemo, LuneOS

PinePhone [$]

Source

An entry-level Linux smartphone.

Released: Estimated Q4 2019
Price: $149
Specs: Allwinner A64 (4xA53), 2/16-64GB, 5Mp camera, 4G modem, ~3000mAh battery
OS: postmarketOS, Debian, Ubuntu Touch, Maemo Leste, LuneOS

PineTab [$]

Source

Entry-level Linux tablet, with similar hardware configuration to the PinePhone and no modem.

Released: TBD
Price: $79
Specs: Allwinner A64 (4xA53), 2/16-64GB, 5Mp camera, ~5000mAh battery?
OS: postmarketOS, Debian, Ubuntu Touch, Maemo Leste, LuneOS

Older and discontinued devices

These devices are not available on the market anymore.

Bq E4.5/E5/E10

These devices came with Ubuntu Touch by default as an option, and are still officially supported by UBPorts.

Released: 2012/2013
OS: Ubuntu Touch

Other older and discontinued devices

2001 IBM WatchPad

You can take a look at LinuxDevices.org for an extensive archive of mostly older Linux phones, PDAs, tablets, wearables and more.