I don't know the answers to your particular question but can share the experience of one person I knew. He came to the US for 6 months with his PI SIM, thinking he would be able to SMS roam. Unfortunately, he didn't send the SMS command to activate the roaming before leaving PI. Needless to say, he was hosed. The only thing he could have done is to mail the SIM back to PI, have someone activate roaming then mail the SIM back. That was maybe 5 years ago. Things may have changed since then.