Bootstrap button: left icon and centered text

I need to generate a button (not a group of buttons) with the following structure:

left-side: [glyphicon] center: Text

example: https://www.dropbox.com/s/3idura8mxf4gekj/call_me.png

Here is what I did:

<div class="row btn-custom">
        <div class="btn-group btn-group-lg col-xs-12" >
          <button class="btn btn-success col-xs-1"><span class="glyphicon glyphicon-earphone"></span></button>
          <button class="btn btn-success col-xs-10">Call Us</button>
          <button class="btn btn-success col-xs-1"></button>
        </div>
      </div>

css:

.btn-custom {
    margin-bottom: 5px; 
}

.btn-custom button { 
    border-left:none; 
    height: 50px;
}

The problem that on a very small screen they start to stack up and don't look like one button. is there any better way to achieve this?

• this code is intended to be used only on a mobile site (m.* url) so please do not recommend me to do other stuff, i know what i am doing.

Thanks!!!