Now spam SMS is no more. Who is there who don't know anything about true-caller application. True caller is the application through which anyone can know the name of a unknown calling number. there are millions of numbers in the database of truecaller, whenever someone calls you true-caller looks up into it's database and appear the name of calling person.
Now this application is available for SMS as well, For SMS it is known as Truemessanger. Through this application you can get the name of unsaved number of SMS sending person, The spam SMS can be blocked by this application. there are already spam number saved in this application which may automatically detect spam messages. True messenger saves messages from spam SMS sender in a separate folder. So you don't need to worry for important received SMS, you can also block SMS country wise and code wise.
Remember it is said about true-caller that they store number from it's consumers means when you will try to sign up to their service they may store your contacts into their database.