phone interview
 

How long usually is a telephone interview? Does anybody have one of those?

It really depends on the type of the interview. For example an HR person might call you just to see if you would be interested in particular opportunity and also to check what salary range you are looking for. This type of interviews (this is not excatly an interview) are usually short.

If you are applying for an IT position and they call you for a technical interview, thw whole thing might last more than an hour, so be prepared.

Lookingforjob is right. It all depends on the job you are applying for.
You said that you'll be applying for HR position so maybe you know the drill already. I don't think it will be more than 30 minutes. I would suggest preparing a list of questions and answers in front of you. This will help you a great deal during the interview.

It's always good to be as much prepared as you can. Create a list with standard questions and prepare an answer for each of them. Be ready for uncommon questions too.

Depending on the job, the phone interview might be short or long. The length of the job interview also depends on your knowledge and your ability to demonstrate it. If the person that conducts the interview sees that you are knowledgeable from the very beginning there is a good chance that the interview will be short and will improve your chances of getting the job.