Old ways don't work any more:
// way 1
void *lib = dlopen("/Symbols/System/Library/Framework/CoreTelephony.framework/CoreTelephony", RTLD_LAZY);
NSString* (*getPhoneNumber)() = dlsym(lib, "CTSettingCopyMyPhoneNumber");
if (getPhoneNumber == nil) {
    NSLog(@"getPhoneNumber is nil");
    return nil;
}
NSString* ownPhoneNumber = getPhoneNumber();
// way 2
extern NSString* CTSettingCopyMyPhoneNumber();
NSString *phone = CTSettingCopyMyPhoneNumber();
Related questions:
Is it possible to detect a phone number of the device in iOS?
[UPDATE]
Provided method works on iOS 6.1.4 without JB and iOS 7.1.2 with JB
Thanks to user creker for hint!
To get number you have to use following way:
1. Code
-(NSString*) getMyNumber {
    NSLog(@"Open CoreTelephony");
    void *lib = dlopen("/Symbols/System/Library/Framework/CoreTelephony.framework/CoreTelephony",RTLD_LAZY);
    NSLog(@"Get CTSettingCopyMyPhoneNumber from CoreTelephony");
    NSString* (*pCTSettingCopyMyPhoneNumber)() = dlsym(lib, "CTSettingCopyMyPhoneNumber");
    NSLog(@"Get CTSettingCopyMyPhoneNumber from CoreTelephony");
    if (pCTSettingCopyMyPhoneNumber == nil) {
        NSLog(@"pCTSettingCopyMyPhoneNumber is nil");
        return nil;
    }
    NSString* ownPhoneNumber = pCTSettingCopyMyPhoneNumber();
    dlclose(lib);
    return ownPhoneNumber;
}
2. Build application without signing:

3. Create xml file (entitlements.xml) with following content:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>com.apple.coretelephony.Calls.allow</key>
        <true/>
        <key>com.apple.coretelephony.Identity.get</key>
        <true/>
    </dict>
</plist>
Where:
com.apple.coretelephony.Calls.allow — for calls
com.apple.coretelephony.Identity.get — for getting own number
4. Sing app with entitlements.xml Copy files in one folder:
./FolderForRunSinging/
    YourApp.app
    entitlements.xml
entitlements.xml - created xml
YourApp.app - binaries for your app copied from XCode files To find where your binaries you can use command:
$ls -la ~/Library/Developer/Xcode/DerivedData/ | grep YourApp
Path should be like this:
/Users/username/Library/Developer/Xcode/DerivedData/YourApp-cktasembftvbmqaaiiunvljdwocs/Build/Products/Debug-iphoneos/YourApp.app
Run singing command:
$codesign --sign='iPhone Developer: FirstName  SecondName (XXXXXXXX)’
--entitlements entitlements.xml YourApp.app
'iPhone Developer: FirstName SecondName (XXXXXXXX)' - name of your certificate in keychain

5. Copy application YourApp.app on your device using ssh to folder
/Applications
6. Restart springboard (run on device):
$su mobile -c uicache 1>/dev/null 2>&1
Working sample could be found on github
Result on iOS 7.1.2 (JB is required!):

Result on iOS 6.1.3 (works without JB and without special signature just build and run)

 
     
    