Things you will need:
- Carrier Sim Card (Verizon, ATT, ETC...)
- WWAN Card compatible with carrier SIM
- Software to communicate with WWAN Card and Sim
Take a look at the smstools, ppp, and gnokii software packages available on GNU/Linux and the BSDs (FreeBSD, OpenBSD, NetBSD). I am currently working on a project integrating a phone system with a pc, gnokii and smstools work well sending/receving sms, mms. have not tried calling though
Some examples I have been able to find that helped me are
-- SMS TEXTING OVER 4G USING SMSTOOLS --
This video https://www.youtube.com/watch?v=sv5zYfwl0wk Titled "Raspberry Pi SMS And Mobile Internet" By Tall Paul Tech And refers to https://whirlpool.net.au/wiki/sierra_advanced
-- CONFIGURING A WWAN CARD ON UNIX LIKE SYSTEM --
This video titled
"The 4G LTE Raspberry Pi Router has arrived! // OpenWrt, Verizon Network" By Dev Odyssey
https://www.youtube.com/watch?v=e4KlUKDai04&t=761s
WWAN configuration is heavily dependent on SIM Carrier, WWAN Card in use, and OS in use - Consult your Operating System manual pages for exact information
-- MANUAL PAGES FOR MENTIONED TOOLS --
Debian man page for smstools - https://manpages.debian.org/jessie/smstools/smsd.8.en.html
FreeBSD man page for ppp - https://man.freebsd.org/cgi/man.cgi?query=ppp&sektion=8
linux.die.net man page for gnokii - https://linux.die.net/man/1/gnokii