How can I use private APIs to block incoming calls in an iOS application?

I would like to be able to selectively block incoming calls in an iOS application I'm writing. This is intended for personal use, not the App Store, so I'm fine with using private APIs to accomplish this.

I have recently come across the Core Telephony framework. Is there a way to use this framework to block calls? If not, what private APIs could I use to do this?

Are you sure it does not? code examples on http://tech.ruimaninfo.com/?p=83 shows how to do such things. Core Telephony headers in SDK are not complete. Of course this means no app store this is my code fragment based on example I linked

if ([str1 isEqualToString:@"kCTCallIdentificationChangeNotification"])
{
    NSDictionary *info = (__bridge NSDictionary *)userInfo;
    CTCall2 *call = (__bridge CTCall *)[info objectForKey:@"kCTCall"];
    NSString *caller = CTCallCopyAddress(NULL, call);
    NSLog(@"Caller %@",caller);
    if ([caller isEqualToString:@"+1555665753"])
    {
       //disconnect this call
       CTCallDisconnect(call);

}

additional definitions needed:

typedef struct __CTCall CTCall;
extern NSString *CTCallCopyAddress(void*, CTCall *);
extern void CTCallDisconnect(CTCall*);

and you need to monitor telephony center's callback(see linked example) I tested this fragment on my iOS5 device

Core Telephony doesn't support this. To my knowledge there is no way to do this with any known private APIs either.