Outside North America, cellphone users make heavy use of texting. It's like a very simple form of email.
Spam's quite rare, because senders are usually charged a few cents for each text. A typical user receives two or three a year. By way of illustration, here's one I received a month ago:
From: Winner
Date: 10/16/04 6:38pm
URGENT! We are trying to contact U.Todays draw shows that you have won a 2000 prize GUARANTEED. Call 090 5809 4507 from land line. Claim 3030. Valid 12hrs only
When you phone the 090 number (a UK phone), you get automatically billed. So in addition to being spam, this is a scam. A fool and his money are easily parted.