"512" is the area code that covers Austin, Texas, and several other smaller cities.
I live in Austin, Texas, and have never heard of "St John Hospital" and cannot find one with Yahoo or Google.
Nothing is listed here either.
http://www.theagapecenter.com/Hospitals/Texas.htm
Texas Hospitals • TX
There is one in Houston, Texas :
http://www.houstonmethodist.org/locations/st-john/
I suggest you go to a hospital near you and ask them if they know anything about this phone number and the details in the mail you got. Otherwise, consider it a scam to steal your identity.
I got email from a hotel they said they need my documents for processing of visa its the same number so forsure its a scam and they have also posted job adds in different job hunting websites