This is a glitch me and my brother found out. It is pretty dang loud to, so be prepared. It also kinda sounds like a Ring Wraith from Lord of the Rings. And all it requires is two cell phones!(We did it with a RAZR and a Samsung Sync, it might now work with other phones.)
Step 1: Get to phones
Things you will need:
( We have only tried it with a Razr and a Sync )
Step 2: Call
Now call the other phone, and pick up.
This shouldn't be to hard, unless your like my brother. =)
Step 3: Call again
Now call that same person again with the same phone, do not hang up the first call, and pick it up also. So now you should have 2 calls on the line.
Step 4: Link the calls
Now the real hard part,(not really.) Link the calls from both phones so that you are in a conference call. Your done, simple enough.
Now for the fun, but loud part. Put it on speaker phone(if you have it. It doesn't make a big difference, it is just louder.) Make all the noises you want. It is fun to make high pitch noises, it sounds like a Ring Wraith. Have fun!
This is my first instructable, so tell me what ya think.