You have to have a U.S. address to get a My Social Security account, but you don't need to have a U.S. address or a My Social Security account to apply for Social Security or Medicare online. And you should use your actual address of residence, i.e. Thailand if you live in Thailand and input your Thai phone number. Manila SSA will email you stating a time they will call your Thai phone number and they will review with you the application you filed online. It's really a very straight-forward process if, as has been said, you're totally upfront and honest with them and don't try to game the system by using a U.S. address or phone number. Oh, there is no problem in applying with your Thai address, phone number, etc and having your monthly benefit deposited to a U.S. bank account.
At the time we applied for SS benefits we were using a Florida mail forwarding service for our address with the IRS and Manila SSA said it wasn't a problem that our IRS address and SSA address weren't the same. They stressed that you have to use your actual physical location as your SSA address, or a PO Box in that location if you don't have secure mail delivery where you live. Since then we've realized that the mail delivery to our condo address is very secure and we've since changed our IRS address, too. The U. S. mail forwarding address is just used for banking, credit cards, investments, etc.