Some older Kindle e-readers will soon no longer be able to connect to the internet to download new books, Amazon has said.
First- and second-generation Kindles did not come with wi-fi functions included, using mobile internet only.
But the slower technology used at the time - 2G and 3G internet - is being discontinued in some places, particularly the United States.
Several other models will also be restricted to wi-fi only.
The mobile-capable versions have historically been more expensive than the equivalent wi-fi-only models.
But aside from that upfront cost, there is no mobile-data bill for Kindles - Amazon pays those fees to keep customers connected to its online store.
The affected devices include models first released as recently as 2016.
Newer ones, which use 4G technology, are unaffected.
"Starting in 2021, some prior generation Kindle e-readers will not be able to connect to the internet using cellular connection through 2G or 3G networks," Amazon told its US customers this week.
The switch-off is outside of Amazon's control, as mobile networks repurpose the older parts of their radio spectrum for faster, more modern standards.
The same situation applies in other countries on varying timescales - in the UK, for example, operator BT has announced it plans to phase out 3G support by 2023.
Other British operators have yet to announce their plans.
The switch-off affects all sorts of older devices, such as 3G-only smartphones.
But such devices tend to be replaced every few years, unlike an e-reader, which may be replaced only once it is completely broken.
Amazon says the first- and second-generation Kindle, as well as the Kindle DX, will lose all internet connection.
The following devices will be able to connect online by wi-fi only:
- Kindle Keyboard (third generation)
- Kindle Touch (fourth generation)
- Kindle Paperwhite (fifth, sixth and seventh generation)
- Kindle Voyage (seventh generation)
- Kindle Oasis (eighth generation)
Those unsure of what model they own can check Amazon's website.
According to The Verge, Amazon has been emailing some affected customers warning them about the change and "thanking them" for being "one of our earliest customers".
It is offering a discount for those who want to upgrade to one of its premium modern models.
It is also possible to "sideload" books on to Kindle, through a Universal Serial Bus (USB) connection, but that requires finding and downloading e-books in the correct format.