Why would I carry .22 mag for defense when a .38 is just as small? I have a .22 LR NAA mini I carry all the time in a "holster grip" in the off pocket. It's deep concealed and never primary, just better'n nothin' if I find myself needing it. I hit pretty well with it, too. It's also a quiet alternative for vermin, snakes, etc, though it's pretty loud out of that 1" barrel. I could carry a .22 mag mini, but it'd just be louder and not a lot more powerful in such a short little gun.
.22s are cool, but I don't consider them adequate for a primary self defense gun. My minimum is .380 ACP and I really prefer at least +P .38.