Gamertag ID

If you just want to swap Live IDs, there's no need to pay to change gamertags. Use a 3rd Live ID to park one of the gamertags on; move the other gamertag to the freed-up Live ID; then move the first gamertag to the now-free Live ID, and the 3rd Live
ID is no longer associate with any gamertag.

Unfortunately, there's a 30-day wait between Live ID changes, so you can't do this all at once.

I think from what you have said this is what you are looking for , try the steps below ..This should help you

If you try to switch your Xbox LIVE gamertag to a Windows Live ID that is already linked to another gamertag, you will receive this message:

“The Windows Live ID you’re switching to is already linked to another Xbox LIVE account. You must use another Windows Live ID.”

Before you can switch your gamertag in this case, you must first remove the existing gamertag from that Windows Live ID account:

1. Create a new Windows Live ID. You will only need this Windows Live ID as a temporary means of moving your gamertags. After the gamertags have been switched, you will no longer need this Windows Live ID.

Example:

Gamertag A is linked to Windows Live ID 1.

Gamertag B is linked to Windows Live ID 2.

Create a new Windows Live ID: Windows Live ID 3.

2. Switch the gamertag that is linked to the Windows Live ID you want to use to the new temporary Windows Live ID you just created.

Example:

Gamertag A remains linked to Windows Live ID 1.

Switch gamertag B to Windows Live ID 3.

Windows Live ID 2 is now free.

3. Switch your gamertag to the Windows Live ID you want to use.

Example:

Switch gamertag A to Windows Live ID 2.

Gamertag B remains linked to Windows Live ID 3.

Windows Live ID 1 is now free.

4. To complete the swap of gamertags between the two original Windows Live ID accounts, you must wait 30 days. (A gamertag can be switched only once every 30 days.)

Example:

Gamertag A remains linked to Windows Live ID 2.

After 30 days, switch gamertag B to Windows Live ID 1.

Windows Live ID 3 is now free and no longer needed.

he can change his tag to the one I already claimed and he doesn't get a id

Just figured it out last time my friend checked both the gamertags first and he wasn't getting numbers and I was but today I checked it first and I did not get any numbers but he did so my guess is that if someone recently checked a gamertag it reserves
the one without a number for them in case they end up taking that tag, so there that's the only reasonable explanation I can come up with for this.

There both unclaimed gamertags