Calls and text messages to cell phones that use any sort of auto-dialer are illegal without express written consent (and the term 'auto-dialer' is applied rather broadly). The same goes for calls that deliver a pre-recorded message. Fines for violations can range from $500 to $1,500 per violation, but you'll have to figure out who's actually calling you in order to file for damages. Almost all of these calls spoof their caller ID, so good luck with that.
If you're in the Do Not Call registry, there are another set of fines on top of those imposed by the TCPA. They start out around the same range, but for excessive violators the fines can now reach up to $40,000 per call (as of August 2016).
Do Not Call registry means that by default spammers are allowed to call anyone not on the list. I guess they paid a lot to politicians to have it this way.
I suppose it had the effect of legitimizing telemarketing at the time, but the effect diminishes as more and more people abandon landlines. Spammers can't legally call a cell phone without express written consent unless they dial the number manually, which of course they never do. That's a protection of the TCPA. Same goes for text messages.
If you're in the Do Not Call registry, there are another set of fines on top of those imposed by the TCPA. They start out around the same range, but for excessive violators the fines can now reach up to $40,000 per call (as of August 2016).