Topping up the minimum $10 every 2 months gets you $60 total yearly cost. Far less than what many spend in a single month for their smartphone plans.
I have been using Ptel for a couple of years now and I pay $10 every 3 months so about $3.33 a month.
Originally I paid $100 for a year and got a free touch phone and out of that $100 I still have like $91 but you have to count that I a adding $10 every three months.
I am on wifi 90% of the time. This works for me and BYOD is great.