Don't mean to ressurect an old thread but on the exhibit2 if you go to the dial pad and type
*#*#197328640#*#* it will shoot you into a tech screen.
Select Debug Screen
Then phone control
then you can select 2100.
*Use the menu button on the bottom left to bring up more options if you click the wrong one and need to go back
** Also if youre in the states select wcdma 1700 it will lock it onto only 4g provided you can get at least one bar.
I have to do this all the time because I live on the edge of a 4g area and will get edge 80% of the time. I lock it onto 4g until I use all of my data then put it back on automatic