What does the o in the corner mean? (pic)

Here is the answer for you;

http://forums.macrumors.com/showthread.php?t=1092855&highlight=circle

 

It means your data connection is GPRS (or 1xRTT), which is slower than EDGE.

See Apple Support Article: http://support.apple.com/kb/HT1976

 

And not in that post, but it's also the slowest Sprint 1X speed.