what input field type forces the number pad mobile keyboard to come up when focused?

Use pattern="[0-9]*"

• Example number input: <input type="number" pattern="[0-9]*" />

• Example phone input: <input type="tel" pattern="[0-9]*" />

Note: Browsers that do not support type="tel" will default to a text type

Beware: Using type="number" can cause problems with some browsers and user experience for credit card, postal code, and telephone inputs where a user might need to enter punctuation or a comma being in the output.

References:

• http://bradfrost.com/blog/mobile/better-numerical-inputs-for-mobile-forms/
• http://danielfriesen.name/blog/2013/09/19/input-type-number-and-ios-numeric-keypad/

The official HTML5 way to handle phone numbers is:

<input type="tel">

You may not have liked the "strange input box" you got with Opera when you used<input type="number" />, but that really is the appropriate type of input area when you want to require visitors to enter a numeric value.

type="number" is HTML5 and many phones do not support HTML5. For call link you can use type="tel" or <A href="wtai://wp/mc;600112233">Special A</A>. You should look at CSS WAP extensions (page 56) too.

EDIT 10/2015:
Most if not ALL smart phones support HTML5 and CSS3, so type="number" is the best way.