Objective C: Function help-Collection of common programming errors

Greetings,

I have the following function:

-(NSString*) nudgePhoneNumber:(NSString*)num{
    NSString *nudged=@"";
    [nudged stringByReplacingOccurrencesOfString:@"+" withString:@""];
    [nudged stringByReplacingOccurrencesOfString:@"\\s" withString:@""];
    [nudged stringByReplacingOccurrencesOfString:@"-" withString:@""];
    [nudged stringByReplacingOccurrencesOfString:@"." withString:@""];
    [nudged stringByReplacingOccurrencesOfString:@"/" withString:@""];
    //NSLog(nudged);
    return nudged;
}

And I’m calling it as follows:

-(IBAction) phoneNumberUp:(id)sender{
    NSString *mob=phoneNumber.text;
    NSString *result=@"";
    [result nudgePhoneNumber:mob];
        ...
}

But I keep getting an exception: “-[NSCFException nudgePhoneNumber:]: unrecognized selector sent to instance” and “Terminating app due to uncaught exception ‘NSInvalidArgumentException'”

I’m quite new to Objective-C and think I just need someone to have a quick look-over.

Many thanks in advance,