It's not obsolete. It is still the only way you can be pretty sure the recipient receives your message since it works on every phone in circulation. This is used heavily by shops online, postal services etc etc.
Many telecom operators also offers basically unlimited texts and calls for a fixed price which makes it often an easier way to communicate than to figure out what service person x is currently on. I use sms way more than I communicate on any other digital service. I would like for everyone to use Signal or something but so far I only have 1 contact there. And by using sms, at least I know it is not indexed and searched by an american company to sell me more ads. Also, I live in a country with large, pretty empty areas. In several of these locations the 3G/4G-networks are often unavailable but sending a simple sms works just fine.