And don't play dumb, randomly texting someone "Go Vote!" is absolutely spam. Texting someone because some sign-up form had automatic opt-in is equally spammy.
Ok, and now someone has downvoted me within seconds of me posting that paragraph; the "I hate people contacting me" crowd is so amazingly vicious :/. Let's look at this from another perspective: I work with a group called Student Activist Network. The entire point of this group is you give them your phone number and they text you when actions come up related to your interests. Much like how anti-email spam people never are willing to believe that some people sign up for mailing lists on purpose, I bet they are also going to refuse to believe that hundreds of activists and protesters specifically want this kind of functionality, and right now the distribution is done manually by people copy/pasting.
A couple people who have my contact information from playing local sports have added me to email lists for causes they care about, which is incredibly irritating. I could see this happening with a texting tool.
I don't know how my number got on these lists, but I replied STOP to every one of them.