Babar Latif sighed,
"Oh Gosh not again."

He said that because this very same question has already been asked - and answered - so many times on this very forum; in fact, two or three times in the last fortnight!!!

So, just browse back through the recent thread titles and look for "GSM", "SMS", etc.
Or try those terms in the 'Search' box.
Not forgetting your favourite Internet Search Engine, of course!