tl;dr -- Most large public services you use (Skype, Exchange, likely Gmail, etc) have backdoors.
Large vendors believe they have to respond to subpoenas or face public obstruction or co-conspiracy charges. As a result, they place these backdoors to avoid the PR or believe they are required to play by the US govt's rules. They may not be realtime backdoors, and they may require a bunch of processing, but it is possible to read most messages sent through large, popular systems (both voice and text like email, sms, chat). I think everyone is waiting for a major court ruling or congressional bill to clarify what's what.
snippet of previous post to explain the vendor's mentality:
> The govt comes by with a subpoena (secret, classified, or public) and requires Microsoft or the customer company to produce communication records that exist in a form that may be used as evidence. Failure to do so is best contempt of court and worst obstruction of justice. No 5th amendment privilege for other people's crimes [and prior to last year's ruling, it was assumed that passwords (or private keys) could be compelled for any reason in the US, and systems were built with that assumption]. So everyone who chooses to store or process messages makes it so the encryption is reversible and they can honor court requests. Nothing is private as a result.
> There is not yet a way to build a messaging service that has both features [content-aware features like URL detection, spell-checkers, web browsing for dumb clients, targeted ads to fund free services, etc] AND [pure] privacy [in the US].