The full specs page for the 3310 says it's a 2G phone. That must be an error? Verizon and AT&T have both started the shutdown of their 2G networks.
You can buy a Samsung/Chinese 3G candybar format phone for $30, which gives good battery life.
Many emerging markets still sell more feature phones and dump phones than smartphones. India for example.
There is even small reverse trend when customers in developed world when people are getting fed up with smartphones.
I'd assume that UMTS would be shut down long before 2g.
https://www.sfmta.com/about-sfmta/blog/why-muni-arrival-time...