Like Pinyin, but I need something that can recognize Cantonese instead of Mandarin. The only Chinese keyboards recognize Mandarin.
or use stroke keyboard.
Or ask Siri. The Cantonese version of Siri can understand Cantonese.
Edit: Apple does not have such a keyboard and as you would know iOS does not allow custom keyboards. Anything suggested is a workaround.
Apple now allows custom keyboards in iOS 8.
https://itunes.apple.com/us/app/cantonotes-jyutping-annotator/id354063453?mt=8 might also work for you.
If you're asking for a jyutping IME you should specifically say so.
From my own research jyutping is quite new and if it has any IMEs at all they are not yet popular and not available on iDevices at all.
The input method that's popular in Hong Kong is called "cangjie". It is based on the shapes the characters are made from and not based on phonetics. I briefly tried to teach it to myself after learning both Pinyin and Zhuyin IMEs but I gave up. It has a much steeper learning curve because there are many principles you must learn. I believe it is much faster for touch typists because it doesn't require (much?) interaction with "candidate lists". But this doesn't help you much.
If you were using an open device like a PC or an Android device you could probably find a Jyutping IME somebody made for their own needs. iDevices are closed and do not allow third party IMEs but maybe you can try to persuade Apple to make one.
I had a look around and there are indeed jyutping IMEs available for just about every OS and device, except iOS. Sorry )-:
If you are a iPhone user:
"Settings -- General -- Keyboard -- International Keyboards -- Add New Keyboard"
There should be four "Chinese - Traditional" keyboards: Stroke, Handwriting, Cangjie, Zhuyin. I recommend Handwriting. You just write Cantonese characters like 冇, 喺, 瞓, etc.. The system recognizes them.
I too try to find out if I can communicate with my friend in Guangdong in Cantonese via iMessage. The "problem" in the end, is about a "national" language versus a "regional" dialect. This matter goes beyond language. I'm proud of being a native Cantonese speaker and I am equally proud of being able to speak putonghua (Mandarin Chinese) which I learned on my own.