Custom Keyboard for iOS

If using HTML5, general approach is to use "pattern" attribute to trigger the appropriate keyboard to appear

http://stackoverflow.com/questions/22867473/how-to-display-a-custom-keyboard
http://bradfrost.com/blog/mobile/better-numerical-inputs-for-mobile-forms/
http://www.html5rocks.com/en/tutorials/forms/html5forms/
https://about.zoosk.com/en/engineering-blog/mobile-web-design-use-html5-to-trigger-the-appropriate-keyboard-for-form-inputs/
http://danielfriesen.name/blog/2013/09/19/input-type-number-and-ios-numeric-keypad/
http://www.wufoo.com/html5/attributes/10-pattern.html
http://blog.teamtreehouse.com/using-html5-input-types-to-enhance-the-mobile-browsing-experience
http://www.bayshoresolutions.com/ideas/blog/improve-your-mobile-web-user-experience-ux-with-html5-input-types/


Developing a custom keyboard

iOS
https://developer.apple.com/library/ios/documentation/General/Conceptual/ExtensibilityPG/Keyboard.html
http://code.tutsplus.com/tutorials/ios-8-creating-a-custom-keyboard-in-swift--cms-22344
http://www.appcoda.com/custom-keyboard-tutorial/