I just moved to Tmobile prepaid plan with 30 dollars (100 min, unlimited everything else). My plan is to use viber and/or google voice. I've been mostly using Viber but I noticed my minutes are eating up for using viber. If I talked for 30 min, about 1 min will count toward my monthly 100 min. Is that usual? My unerstanding is these calls through viber should be completely free since I am just using data. Or is there something I am missing? Anyway that I need to instal or setup viber so that it is completely free.

Thanks so much in advance.