Similar to the popular F.U.P.A this is a reformed and politically correct version of the term. UGA refers to a Upper Genital Area, and is meant to be preceded by an adjective such as 'fat.'
A person that is particularly DEXTEROUS at sending TEXT messages, preferably using only one, or at most two, thumbs. These people can send out messages at seemingly unbelievable speeds, amazing those around them with their deftness.
Chad was texterously churning out the messages - his thumbs were just a blur over his phone.