Intego's "Year In Mac Security" Report
david.emery notes the release of Intego's "Year In Mac Security" report (PDF), adding: "Mac OS X and iPhones that haven't been jailbroken fare pretty well (although vulnerabilities exist, there's not been a lot of exploitation). Apple does come in for criticism for 'time to fix' known vulnerabilities. Jailbroken iPhones are a mess. The biggest risk to Macs are Trojan horses, often from pirated software."
I'm not sure what you mean by "basic functionality".
My iPhone isn't broken and I have tethering enabled. Sounds like your problem is with AT&T. I'm in Canada under Fido/Rogers so YMMV.
With "both" companies my tethering is enabled with a quick call. My provider asserts that my data plan must be 1 GB or higher, but this is largely to protect me from ignorantly going over my data plan usage allowances. I go to my settings and turn on tethering. There is no step three ;)
As for "applications that Apple doesn't [sic] like", you must mean malware, trojans, and data theft mechanisms. If you want to run those by all means do so. You could save yourself some trouble and just write your date of birth and credit card numbers on a placard and hang that around your neck when you head to the mall.
But I keed.