I've noticed that when sending BTC via SMS, if the BTC are not claimed within a certain amount of time, they disappear.
Here is an example from my own account.
As a test, I sent 1 BTC to my own cell phone number and intentionally never claimed the BTC.
Now when I check my wallet history or click the link from the SMS, it says that the funds are gone.

This is the first time I confirmed it %100 for sure, but I am 99.9% sure this has happened with lots of other Bitcoins I have sent to people who didn't know how to claim them.
Can you let us know what is happening to these Bitcoins?
How's the new server?
HANG HIM HIGH!!!
Ok, wait for what he has to say first

I sent 1BTC at a time to many many people via instawallet but I bookmark all these urls and tell them that to claim the bitcoin they have to move it out of my control as else I will take it back after a month assuming they are not interested. Actually I took back almost all of them and would be very pissed to see instawallet doing that instead of me. Luckily this does not mean that almost all of them did not get interested. Many had a lot of questions and stayed in touch over 10 mails but they never took the coin that I offered them to try it out.
Instawallets statement about keeping the coins available is also very interesting. They told me here on the forum that there is no timeout and all wallets will be kept available indefinitely and if they ever end operations, they will send all the bitcoins into brain wallets based on the respective url. Clever clever
