I interviewed with a company two weeks back and got an email this Monday that "You can expect to hear back from another employee with an update shortly." Its the 4th day now, but two days out of the last three(Monday and Wednesday) I was travelling in an 8 hour flight, so I don't know if they called me or not.(Though I don't have any voicemails). Now I'm confused as to should I follow up again? May be they called me when I was in the flight. Or maybe not. "Shortly" for me seems to be pointing to the same day. What can shortly mean here?
Be patient. It's hard for all of us, but 4 days is short in the world of HR.
They would have left a voicemail if they wanted to reach you. So they probably have yet to call. Personally I wait one week before I follow up with a call. Depending on how well your interview went, you should call them soon if you don't hear anything.
But to directly answer your question, "shortly" can mean anything from a day or two, to never hearing a reply.
Honestly, HR has no idea when it is going to get to you. Sometimes they never do. Companies are pretty horrible with this and it has only gotten worse.
In my experience, the bigger the company, the longer it takes to get back to you. Startups usually take a day or two to decide, where as my current company (multinational) took about 3 weeks.