I'd like to make the background image for my input field disappear once the user has typed any amount of text in it. Is there a simple way to do that in javascript? I can get it so the bg disappears while the field is focused, but then it returns once they move on to the next field.

HTML:
Call me at <input name="phone" type="text" class="phone-field" id="phone">
CSS:

.form input {
  background-color:transparent;
}
.form input:focus {
  background-color:#edc;
  background-image:none;
}
input.phone-field {
  background-image: (url/images/phonebg.png);
  background-repeat: no-repeat;
  background-position: left 1px;
}