Nothing happens when trying to dial a number

I'm trying to programmatically dial开发者_如何学编程 a phone number on iPhone by running this command:

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"tel:555-555-5555"]];

But, nothing happens, as if the command never ran.

Any ideas?

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I'm not sure the simulator allows you to place a phone call.