Toronto police have issued a warning about a fraud and extortion scam in the GTA that involves threatening phone calls or text messages from U.S. phone numbers.In a public safety notice on Monday, police said the text messages contain "graphic violent images," but they did not elaborate.The calls and texts are from American phone numbers with the area codes of 470 and 404, police said. Both area codes are found in U.S. state of Georgia.Police said the scam is being reported with increasing frequ