By the way, there's a centralized DND registry in India called "Commercial Communications Customer Preference Portal"[0]. You just need to send an SMS to enable/disable unsolicited commercial calls/SMS. It has been very effective so far.
It's a pain in the ass but I kept on reporting for a month after activating DND and the calls and messages dropped. I've even received calls from people begging me to take my complaints back or otherwise they'll loose their jobs. I agreed twice but holy hell those exact same companies spammed me again. I stopped being a good samaritan and just told them to sort it out with their companies since it's the companies fault. Now spam has reduced to a message or two a month.
From what I understand there are old mobile numbers list being passed around from before DND was available and that's why you need to start reporting the spam messages. Word quickly spreads between the companies to remove your number from the lists.
In the USA, T-Mobile spammed me like this. Again, very difficult to stop the spam.
I think eventually this will be unstoppable, at which point I guess I'll stop using SMS and/or stop using phones.
I can't wait 'til the day I'm sitting in a group, and everyone keeps pulling out their phones every 30 seconds to clear another SMS spam, and then call me a luddite when I say I don't have a phone.
Data is much better now, coverage is very good in metros, and sucks outside, but that's fine with me. Guess if you live in certain areas (e.g. Los Gatos, CA) you might have to get VZ or something - though I hear they're doing a lot to fix that (e.g. band12 LTE using 700Mhz spectrum).
Essentially, you will get several sms messages a day which if you accidentally hit one of the keys on your phone ( which is actually very easy ), you get billed $1 every week ( think daily fortunes / love poems / etc ). It's very easy to accidentally opt-in to several of these.
To opt-out of these advertisements you need to find a hidden number on the telcos website, send an sms message, and wait 10-14 days until the advertisements stop.
I have to think that the telcos are taking in millions of dollars every month from these spam ads.