Actually, this is generally possible with the native behavior of the device - in a native app.
In a webapp or native app with webview, you are at the mercy of the browser. No browser I know of exposes this ability. You would need separate input fields for the numeric and text parts.
If you are writing a PhoneGap app, you could write a native extension to do this, but will need to write it in the one of the native languages available on each device (typically, C, C++, objectiveC, Java), you will have to re-write it for each platform you want to support.
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