Boost and Virgin are owned by Sprint, which run on the Sprint CDMA network. There's no GSM network for any of them. Verizon is the other carrier with a separate CDMA network. T-Mobile and AT&T each have their own GSM networks.
ETD means that the Eustachian tube is blocked or does not open properly. Air cannot then get into the middle ear. Therefore, the air pressure on the outer side of the eardrum becomes greater than the air pressure in the middle ear. This pushes the eardrum inward.
Eustachian tube problems and the associated ear infections are among the most common problems seen by health-care professionals. Many people have chronic problems regulating middle ear pressure. The Eustachian tube can be blocked, or obstructed, for a variety of reasons. The most common cause is a cold (upper respiratory infection).