there's discord-wap which is a self hosted discord bride that translates discord into wml 1.1 which is readable by wap browsers

i vibecoded a signal-cli bridge but it's embarassing to say the least and it's a security nightmare (at least it works)

depending on what kind of phone you use there's either a csd or gprs connection.

both need a working gateway

a user named bs0dd made a comprehensive guide on how to set up a gateway and even setting up your own dial-up connection for older csd phones.

csd is hard to setup though, in my country (germany) it only works with vodafone sim cards or (as i currently do it) you can connect to a foreign dial-up connection, some of these still exist lol

i would suggest looking into the reddit community /r/vintagemobilephones and especially their discord. the community is very active and currently still working on projects