Mosty companies that do things on the cheap with SMS make their revenue by selling on mobile numbers to Telemarketers around the world, as they have to pay the individual telcoms they use, the same as everyone else for using bandwidth.
I prefer to pay a bit extra in order to know my number is secure, but that is my choice.
When you hear someone say, I keep getting marketing calls on my mobile, how the hell did they get my number? That will be because of the service Baboyako used, passing her friends private numbers onto the world telemarketing database.
If you SMS with Skype, the reply goes to my mobile.