"This week, CNN interviewed Tim Clemente, a former FBI counterterrorism agent, about whether the FBI would be able to discover the contents of past telephone calls between Tamerlan Tsarnaev and his wife. Clemente stated that the FBI had ways of accessing those calls, and that all calls are recorded."
Not just can the government start recording a particular suspect's calls. The old calls, from before they noticed this guy, are already recorded, and so are yours and mine. That's what Clemente says, anyway.