tmobile/$30 plan user here
1.i gave my friends my google voice/grooveIP as home phone number, so i save minutes by using it at home as often as possible.
2.i use over 100 mins here and there, but then i consider it as $30 for 100 mins, $40 for 200 mins, $50 for 300 mins plan. for someone who barely uses 300 mins, $50 for 300 mins/unlimited text/5GB is still a good deal for me. $.10 per minute may seem a lot but not a big deal for me. i just have to be careful and have some credit in my account though.
3.i doubt i'll ever go with LTE until its battery-eating problem goes away. i would hate the idea of turning 4g/LTE on and off again to save battery life.
4.sprint 3g is close to 2g where i live. sprint's prepaid divisions are hogging datas everywhere, slowing down everyone's speed.
5.haven't used more than 3gb of data a month, with lots of wifi-usage at home. still 5gb is a lot for $30 and i'm not sure if i'll ever take advantage of unlimited data plan. this is just me though.
anyway i'm very happy with tmobile's $30 a month plan and i hope it never goes away.
i do get slow data speed from time to time though, especially in university campus. i can live with it.