To my knowledge MotoWebKit on ET1 doesn't support <input type="number" or <input type="tel".
May be you can force the app to use device browser. If the ET1 uses JellyBean then the browser is much better than ET1 GB.
Rho 4.0+ version on Android devices use the native engine and should allow for more input types like number, tel,...
Another option is to create a JS popup key board that way you have complete control over the keys and validation.
Herb Turzer suggested Hacker’s Keyboard which worked very well for what the customer wanted.
Simple configuration and a truly "free" app. No ads, no GMS required, etc.