The stock browser crypto algorithms are too old to connect to most sites, practically zero apps of use support anything that old, you aren't going to be running Firefox or Chrome unless you grab an ancient build. No WhatsApp, Signal, etc. The majority of stuff on F-droid doesn't run, the camera is terrible, it has basically no app storage and you have to use that old mod which allows an ext partition on your SD for apps, which is _slow_. I'm really not sure could find a single practical use for it.
I'm (hopefully) getting a Librem 5 phone sometime this year but I already know it's going to disappoint even as I've been expecting as much from the start. You're not getting these phones for their practical superiority on any metric, but as a weak signal to the world of an approach you'd rather others took, and maybe this will help form a better bedrock for yet another attempt in another 5+ years especially given how much upstreaming is going on vs. what Mozilla or Ubuntu did. I think the Librem is even more disappointing than the PinePhone (which, given its much more reasonable price, I'm tempted to buy for the same reasons I'm getting a Librem) and that's only comparing with my Note 3 let alone some of the monsters out there now (16 GB of RAM on a phone exists). The Librem/PinePhone have as much RAM as my nearly 8 year old phone, same number CPU cores (but lower frequency and probably lower performance), same internal storage, in the case of Librem actually more money in nominal prices, both lower screen resolution, uncertain whether Librem'll survive carriers moving to VoLTE (my Note 3 will)...
My only point in this mini-rant is that while it may not be a 10 year old phone, at 8 years my Note 3 is still looking better than these 'new' things on feature set. GP is right that these open phones are disappointing, even if in some cases there's nothing to be done because of the higher level project goals.
It's tri-band, but I only use it on wifi. I might be able to compile newer firmware, but the Android SDK has never worked for me even in the most casual use, so I never tried.
A decade-old phone would run Android 2.3.7 (Gingerbread), have a dead and unchargable battery, no longer support modern SIM cards which is fine because its odds of connecting to any modern networks approach zero as the old spectrum gets recycled, be unable to run any recent apps (ancient OS version, no memory) including not being able to run any browser capable of opening modern websites, and would have a slow clunky UI on a cramped little screen. The PinePhone has a long way to go, but it would destroy any decade old phone in very nearly every comparison.