TTStyledTextLabel is exactly what I want, but I don't want to add all Three20 project just for this only one function.
Any suggestions?
If you are OK with limiting the application to iOS 6+, Attributed string support is available on all standard rendering controls, if not, there are many other 3rd party solutions available (including my favorite, OHAttributedLabel). Just don't use a WebView for something this simple, they are really really heavy objects.