Natan, It should work like this already on the Contact Details window. You get a different icon on the left depending on if it is a "phone" or a "cell/mobile". When the phone number is also associated to a context (home, work) you will also get a different icon on the right. All the icons can be customized by editing the style sheet.
If you don't see them it may be related to an "issue" first reported yesterday that I am still investigating. What is your phone "device language"? Italian? Felipe