What features am I missing by using a non-smart phone?

So the other day I sent in my Pixel 4a to get the battery replaced (probably should have saved my money for a new phone, I know). But anyhow, while I'm waiting for the repair, I've been using my ZTE Cymbal Z-320, not-Android, no app store, flip phone.

But as soon as I stuck the SIM card in there and fired it up, I got a message from T-Mobile that I would be able to get their services on this phone.

Now, I'm wondering if they're talking about data. But on the other hand, maybe on-device voice mail. However, the voice mail hasn't worked for months, if not years on my Pixel. I can dial in, but the Pixel couldn't connect to download new voicemails on the device itself. So I'm just guessing what other services I'm supposed to have that I'm supposedly missing out on by using an old flip phone.

One thing I love is I turned it on on a Thursday and didn't need to charge the thing until Monday. I never hardly use the Pixel for anything other than phone calls, but it was getting very bad, going from 100% to about 20% in 8 or 10 hours without even using it.