Every other year or so, but only because there somehow keep being better deals. Over the last 8 years mint mobile has been consistently good pricing even for returning customers provided you're willing to pay for the whole year up front. That's my baseline. From there other small carriers come along offering unlimited for less and you join for a year or two until they go bust. Right now I'm on Spectrum mobile since it's free with even the cheapest home internet available to my address (for 12 months).