I would like to suggest "double" addons: $5 to double the data allowance included in the base plan, $7 to double the minutes, and $10 for a "double-double" that doubles data, minutes and texts included in the base plan. (The latter one is of limited appliccability to current price plans as there are no plans that have limited texts AND a data-allowance. But there might be some legacy plans, dunno. And in case it would be easier for marketing that way.) Of course I don't have the data to simulate the effect on the margin, but I'm sure it would increase the ARPU.