Back in May, the Australian Communication and Media Authority (ACMA) reported what you and I already knew: "The complexity of plans and how they are framed make it virtually impossible to compare them accurately." That got local price comparison site, WhistleOut, crunching the numbers, and the result is this fantastic infographic.
Over in the US and UK, mobile phone plans are largely advertised with the minutes of calls you receive per month. That definitely helps when you're making comparisons. In Australia though, 'cap' values have over time become confusing at best, and misleading at worst. The gradual shift to 'Unlimited' voice plans (dubbed Infinite by Vodafone, for instance) have helped matters, but there's still a lot of plans out there.
Focusing only on converting talk time "value" to "minutes", WhistleOut used the total monthly value on calls, but didn't factor in text messages. You may also note that they haven't included free calls: Virgin to Virgin or Vodafone to Vodafone, for instance.
Calculations used by the self-described telco-independent site did assess call rates, flagfall charges and data plans. Call lengths were averaged to 3 minutes. [WhistleOut]