< resources >  
    < string   name = "hello" > < u > phone: 1390123456 </ u > </ string >  
    < string   name = "app_name" > MyLink </ string >  
</ resources >

 <resources>
    <string name="hello"><u>phone: 1390123456</u></string>
    <string name="app_name">MyLink</string>
</resources>

TextView textView = (TextView)findViewById(R.id.testView);  
textView.setText(Html.fromHtml("<u>" + "hahaha" + "</u>" ));