iOS: phone number dialing not working

Question

I'm building an app that lets you call different service centers from Netherlands. The problem is that some of them have a different commercial format (like 0800-xxxx) and the device can't make the call. The code looks like this:

if ([[UIApplication sharedApplication] canOpenURL:phoneURL]) {
    [[UIApplication sharedApplication] openURL:phoneURL];
}

Do you have any idea how to format the number or to make the phone call, no matter it's format?

EDIT: This is how the phoneNumber is created:

NSString *phoneNumberString = phoneNumber; // dynamically assigned
NSString *phoneURLString = [NSString stringWithFormat:@"telprompt:%@", phoneNumberString];
NSURL *phoneURL = [NSURL URLWithString:phoneURLString];

Answer 1

I used this code and it worked:

NSString *cleanedString = [[phoneNumber componentsSeparatedByCharactersInSet:[[NSCharacterSet characterSetWithCharactersInString:@"0123456789-+()"] invertedSet]] componentsJoinedByString:@""];
NSString *escapedPhoneNumber = [cleanedString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSString *phoneURLString = [NSString stringWithFormat:@"telprompt:%@", escapedPhoneNumber];
NSURL *phoneURL = [NSURL URLWithString:phoneURLString];

if ([[UIApplication sharedApplication] canOpenURL:phoneURL]) {
    [[UIApplication sharedApplication] openURL:phoneURL];
}