Petunias are an annual. Having one last for many seasons is an aberation not the norm. Freezing is not why they die. A petunia is realitivly frost tolerant. They die because their normal life cycle is that they grow, bloom, set seed and die in one season.

However if you want to keep certain varieties you can take cuttings, root them and plant them and it is a new plant with new roots.

To take cuttings, cut about a 4 or 5 inch piece from the growing tip. Cut just below a leaf, dip the cut end in rooting hormone and place it in moist--not overly wet--soilless mix in a pot. Keep it in a sheltered place where it gets light but not direct hot sun. In week or 2 you will start to see new growth and you'll know it is starting new roots. Wait a couple of more weeks and you can replant

That's not really correct, the standard annual petunias you get from the home centers are annuals, but the Wave, Surfina and the possibly the Supertunia are annual - perennial hybrids.

So you can't say that they pure annuals and the websites say they are hardy in zone 10-11 (I'm zone 9 but the USDA zones don't work well on the west coast because of marine influence).

I was hoping someone with experience from a hot climate would reply but I know it's along shot.

Also, typically about 1/2 - 1/3 of my annual petunias survive a second season - I can show you pictures. The whole annual/perennial classification can be blurry for some plants. Lots of "annuals" are completely perennial here(w/o reseeding) and as you know some perrennials will only last 2-3 seasons. For example annual Lobelias here are known to last more than 1 season w/o reseeding although the performance slowly declines.