http://www.forbes.com/sites/andygreenberg/2011/08/12/codebreaker-karsten-nohl-why-your-phone-is-insecure-by-design/
a bit heavy content at times, but "code-breaker" guy tells us what he and others have found ... but he can only speculate why it is the way it is.
Glad to see that there are still white-hat hackers that break things to show they can be broken and need to be improved, instead of to steal people's identities.
Interesting reading so far, given how fast cell phones proliferated over the last 20 years I'd be surprised if those systems were NOT a labyrinthine mess...
iOS 5 'Unsecured Calls' warning lets users know if they are talking on unencrypted networks
http://spybusters.blogspot.com/2011/06/new-feature-in-iphone-ios5-unsecured.html
fyi the white hat in the OP as identifying the so-called "secured" protocols as ... not so much. But also yes it seems some carriers or regions will be truly "un"secured communications. yikes. Makes a certain Pulp Fiction telephone scene come to mind ;)