A little more info I gleaned from the Folsom PD Facebook page (you don't have to be on Facebook to see it):
What the PD used was called Everbridge, which only notifies landlines in whatever area or addresses the PD specifies. If you want your cellphone to receive these kind of alerts they have a link on the Facebook page to the city Website where you can register so you can get the alert on your mobile device.
Thanks for the info. I know the city has my cell number because they called me in the middle of the night once to let me know my backyard fence was on fire, but I just made sure that all of the info was correct and up-to-date.