You’ve likely seen people post twitter messages with special symbol characters like music notes (♪ ♫) indicating their tweet is referencing lyrics from a song. If you are already familiar with these symbols then you know these are actually HTML character codes which were introduced as of HTML 4. These symbols were likely entered via the web, but if you have an iPhone you can now send these from your phone!
The iPhones international keyboard gives you access to the Japanese Kana keyboard, enabling lots of symbols that are inaccessible from the standard Western keyboard. These symbols include mathematical symbols, circled/uncircled numbers, weather symbols, card suits, arrows, and more!
To better illustrate how to access these here is a quick little video, enjoy: