What does the 'Mark as default' option do in my 'Edit' option of a contact What does the 'Mark as default' option do you can choose in the menu when you select a contact which is present in the phone memory ?

I am seeing this on a Samsung Galaxy S phone ( if this should make a difference ).

-- background information (for those interested) --

I am still trying to copy phone numbers one at a time from SIM to the phone memory ( see my other question ).

At the moment the easiest way to accomplish this is to send the contact information using the Send via + Gmail to my own Gmail account, press Download in the received email and choose Contacts ).

Having done this for the few numbers I wanted to transfer ( it's main reason being that I now can attach a picture and a ring tone to the important phone numbers, while still retaining these numbers on my SIM card should my phone suddenly die ), I now noticed the 'Mark as default' option in the menu of a phone number saved to the phone memory.

Before selecting this option, I wanted to ask what the option will actually accomplish.
I'm looking for documentation to back this up, but in my experimentation the "default" phone number for a contact is what's used with voice commands if you don't define a phone "type".

So, if I have three phone numbers for John Smith, if I just use the command Call John Smith the default phone number will be used. Otherwise, I need to use Call John Smith home or Call John Smith mobile.

It's also used if, when looking at a list of contacts, you tap the phone icon next to the contact's name. It will use the default phone number (if defined).