According to my experience, there is a no legally way to buy a list of phone no. but if you are from India then you can find categories, city wise from JUST DIAL, here you find all contact with their address and it helps you to grow your business. If you buy from somewhere then it’s not guaranty they all no. is correct. So, I suggest don't buy from anyone
We’re firm believers that the follow-up is one of the most important elements of the selling process. After you fire off an email looking for an approval or confirmation, a short follow-up by text could be the perfect nudge to get your prospect to take a look. Remember, since 90 percent of text messages are read within a few minutes, there’s a good chance your SMS follow-up will be seen right away and prompt your prospect to answer.
Please take everything I have mentioned above seriously or you might end up well let’s just say in some kind of trouble. So my advice to you sir would be to engage service that operates out of US soil for example Europe but that is capable of providing you service where you need it. A perfect fit for this would be Hottelecom. More details can be found here.
Marketing through cellphones' SMS (Short Message Service) became increasingly popular in the early 2000s in Europe and some parts of Asia when businesses started to collect mobile phone numbers and send off wanted (or unwanted) content. On average, SMS messages have a 98% open rate, and are read within 3 minutes, making it highly effective at reaching recipients quickly.[4]
The main and the most primary factor that makes social media better is that, from social media largest companies can get the direct response from the customers, we can say that social media is now playing its role in shaping the perception. Social media has gone through changes; primarily social media has been used for the sake of entertainment. Entertainment seeker looks for the funny videos, songs and sometimes documentaries.
  Most of the world are beginning to think that sms marketing tools are going to take over the way we do business both online and offline? If you would care to consider the fact that an average of 97% of recipients open their text messages. That stat is crazy! A person on average check their cell phones at least 50-100 times a day. Why don't you try an pay attention to how many times you look at your cell phone on a daily basis. It's a lot right? 
Once you've collected your mobile numbers, verified that you have followed all of your legal responsibilities you can start your SMS marketing campaign. I'd suggest using a 3rd party service provider to ensure that you are able to track the return on investment for your campaign, embed an unsubscribe message, and easily manage your SMS marketing database including unsubscribes.