Orange Pi 2G-IoT was unveiled at the start of the year as an ultra cheap ($10) Linux development board with 2G cellular connectivity. The board has just launched for $9.90 + shipping on Aliexpress.
Linaro showcased Ubuntu on the similar Orange Pi i96 board at Linaro Connect Budapest 2017 last month, but I have not been able to find an image, nor source code yet. Needless to say, beginners better wait before buying this board, as everything is new, and software support is unclear at this stage. You’ll also have to check 2G sunset status in your countries, as some have stopped supporting 2G already, while others plan on keeping 2G networks for many more years.