They text you in a way as if they know you. After a "hi (your name)", they try to ask you things like "how ya doing?" to engage you, getting your interest or openness. It gets my suspicion instead, though. I get many of these from other callers.
Received a text that said "Hey :)" When I responded, "who is this?" They tried to get me to add them on yahoo messenger. I again said "who is this?" They said "no reception :(." I typed the number online and found this. At that point I replied to them that "I see its a prank caller and they have nothing better to do with their life."