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.
Ear Congestion. Another duty the Eustachian tube has is to help drain fluid or mucus out of the ear. However, if the tube becomes inflamed from an infection, this task becomes much harder. Trapped fluids build up and place pressure on the eardrum and other surroundings.