Back in 2010, I bought a phone, what's the simplest, It is wirelessly connected with its phone base linked to a phone socket.
I can use it battery or main operated.
In europe, it's a standard that make the stream between the phone base and the handset. This european standart did'nt change a lot since 2000. And I explain why.
Like you guess, nowaday, the phone models come in the tech'store as soon as they leave it. I had to say that my old handset model is no longer in some tech'store.
I even try to add a handset to the old phone base although I was skeptical. I didn't want to waste in buying a new whole phonebase/handset package. I was trying and, with a great astonishment the new handset perfectly connected to the old phone base. The standards don't change a lot. And the european standard of indoor wireless communication follow the rule. The new handset associated very well with old base.
Peering of my new handset
The button that are pressed to open the acknowledgment of a new handset are often hard to find. And the phone base manual talks about the "Paging" word to add a new handset, it's the common tech'term. Moreover, they are so hard to find that I can say sometime it's likely imossible to find them or make possible the association.
In my case, the "Paging" button is on the top left of all other phone base buttons.
Then, according to the handset models, it's likely what follows: