If you're trying to send mail to subscribers at clear.net or clearwire.net today, you'll notice that all delivery attempts are being rejected, because wireless data provider Clearwire has retired all email services as of April 15, 2015.
Once upon a time, Sprint was the biggest investor in Clearwire, and Sprint's 4G data service was provided over the Clear WiMAX network. Sprint fully acquired Clearwire in 2013, and announced that it would be shutting down the Clear network sometime in 2015. It stands to reason that this email domain retirement is likely related to that overall acquisition and service shutdown.
I was not able to find any information related to the transition of clear.net or clearwire.net subscribers to other domains.