linuxmemes

I think you're misunderstanding it. Most mobile apps have sensible defaults regarding data and battery usage, for instance, not updating (their feeds/server status/whatever networked service the app uses) if not in WiFi.

I'm talking about stuff like pulling down new podcast episodes and such.

It'd theoretically be possible to run a straight GNU/Linux tablet or laptop

"GNU/Linux" is the full way to say what sometimes gets shortened to "Linux"

a family of operating systems based on the Linux kernel and a lot of software from the GNU project. This explicitly distinguishes it from Android, which also used the Linux kernel.

The former is not, in 2025, typically used to run smartphones. The latter is the most-common smartphone operating system in the world. If you buy a smartphone that isn't an Apple smartphone, it almost certainly runs Android.

with a 5G cell modem for data

5G is the current generation of cell phone radio protocols. Communicating directly via voice over this protocol is not something that I believe is available to GNU/Linux in 2025. However, it can send non-voice data.

, use SIP service

SIP is a protocol for running voice over a data connection to the Internet. If you have an Internet connection, you can use SIP. There are companies, SIP service providers, which will, for a fee, provide a phone number at which one may be called or call others from a computer that can make use of SIP.

and a GNU/Linux dialer,

A dialer is the piece of software that on a smartphone, a user would probably call something like "the phone app".

and then run Waydroid for any specific Android apps that one has to run.

Waydroid is a piece of software to run Android apps on a GNU/Linux system.

Idle power usage is gonna be a lot higher than on a phone, though.

Phone hardware and software has had a lot of work put into optimizing it for very low power usage. A larger device, like a laptop or tablet, will probably also have a larger battery, but it will consume more power as well.

And a lot of Android apps are made with a touch interface

Smartphones, due to physical space constraints in one's pocket, typically have an entire side be a touchscreen. They do not have a keyboard. In general, software optimized for this works somewhat differently from software optimized for use with a keyboard and mouse.

Most GNU/Linux software is written with the intent that it be used on a system that almost certainly has a mouse and keyboard available. Most Android software is written with the intent that it be used on a system with a touchscreen available.

This means that even if one can run GNU/Linux software on a phone, much of the (large) collection of GNU/Linux software available will not be designed with an interface ideal for use on a phone.

and small screen in mind and are aware of things in a cell environment, like "only update X when on WiFi". Not really common for GNU/Linux software to do that.

Smartphones have two widely-used mechanisms of accessing the Internet

connecting to the often slower cell network, or to a much-shorter range, but faster, WiFi network. Many people connect their smartphone to a WiFi network at some times and a cell network at others. Because this is so common, a lot of Android software has behavior designed to support this and act more-appropriately, like having an option to only transfer lots of data when on a WiFi netwprk. This is not the case for most GNU/Linux software.

Waydroid is a android translator(?) for linux on wayland, it runs android applications in a translation layer (android has linux under it), so you can install a ROM (there's a default one without google applications like google play services, but you can search a ROM with it) and run android applications like any phone with a custom ROM.

Edit: The tablet with waydroid running:

*liquid▶️ass