INS will send ACK
The acknowledgement depends on what your attorney preferred notification method when they filed your premium processing.
Usually, email/fax. In the ACK, it will give you a case number. There on, you can check your status online, by phone or email. Premium processing filers are give a special phone number and email address. You can find that in INS site.
ACK will be sent out soon after INS receive the petition, i.e. usually the day/next day they receive the petition.
Hope this info is correct...
