It's possible to send an e-mail which a phone receives as an SMS by sending to (in the case of Verizon) [email protected], and when I use the SMS app to send to an e-mail address, that's what shows up as the sending account. (This site has a list of the "@telcoName.com" addresses for various other carriers.) Is there a way for an app to know that "[email protected]" address of the phone that it is on, WITHOUT having to send out an e-mail over SMS first and then be told whom its sent message came from?
Is there a particular permission that a developer would use to determine this info?
With some other research, it appears that the answer is NO: the phone does NOT "know" the email address that will reach its SMS app. This info can be determined by asking the user his phone number and cellular carrier (looking up the "@whatever.com" part in the website I posted in the question), OR you can have the app send an SMS to an email address on a cooperating code server, which then "tells" the app what email address it just got a message from.
But the Android operating system in the phone doesn't have this information available itself, so the app can't get it from the OS.