It's easy to clone dinosaurs from frogs, if you're in Jurassic Park. ;)
That said, there is an argument to be made that amphibians don't learn socially, so a cloned frog is as good as a "natural" one... and since some amphibians can change sex, they might be able to clone than other classes.
However, there is resistance to cloning as a solution to extinction as you lose social/behavioral knowledge that animals with more complex neurology have (this happens in captivity too). You're also put into a situation where to add genetic diversity to the genome, you basically have to induce mutation instead of relying on those that have already been tested by evolution.
Oh yeah. Jurassic Park. That's probably it.
I would hope someone has tissue samples frozen away. Someday, it should be possible to restart the species. For that matter, if there are extant frog corpses around, their tissues should be sampled, as well.