This is more for the ladies, but...
It's legal: cops seize cell phone, impersonate owner 
"In November 2009, police officers in the state of Washington seized an iPhone belonging to suspected 
Prohibited Subject. While the phone was in police custody, a man named 
Prohibited sent a text message to the device, reading, "Hey whats up dogg can you call me i need to talk to you." Suspecting that 
Prohibited was looking to buy 
Prohibited from 
Prohibited Topic, Detective 
Prohibited replied to the message, posing as 
Prohibited. With a series of text messages, he arranged to meet 
Prohibited in the parking lot of a local grocery store—where 
Prohibited was arrested and charged with attempted possession of 
Prohibited subject."
http://arstechnica.com/tech-policy/2...ersonate-owner
The full legal opinion the above article is based on can be read here: 
http://scholar.google.com/scholar_ca...,5&as_ylo=2012