Step one, don’t do it. Remote interviews are not as effective as in person. If there is a way to conduct the interview face to face, then take that option.
Unfortunately, in today’s distributed work environment, remote interviews are becoming more common. Thus, it is worth looking at some options to make them as effective as possible.
If you can’t be in the same place as the candidate, at least make sure you can see them. Video conferencing is a must for a remote interview. If one of the criteria you are measuring in the interview is communication (it should be), then you will need to see how they make eye contact, how they make use of gestures and how animated they are while making a point.
There are many options for video conferencing, and if you have remote offices you should already have them in place. If you are looking for an option, Skype is a good starting point as it includes video, screen sharing and chat features.
It is unclear to me as to whether it helps to have a person with them at the remote office. If is is possible to have someone from the team or department they will work in participate, then that can be helpful. Otherwise, just have someone show them to a room setup with your video conferencing. The other option is to interview the candidate at their home, and this may be the only option if they are remote from any of your offices.
For asking technical questions where you want the candidate to sketch out a solution, EtherPad is a good option. The main advantage is that there is no setup involved. You can send the candidate a link and they can start typing. Google Docs also has collaborative editing feature
In a recent interview, we used this approach for asking some basic programming questions, the type you may do on a whiteboard if you are in person.
For this type of scenario, it is best to have two screens or computers available to you, so you can continue to see the candidate on video while watching them type in their responses.
One of the nice features of EtherPad is that you can replay the session afterwards based on a time slider to review any section.
Be aware that when setting programming questions that you may be Google hacked, as the wise candidate can research typical questions ahead of time. Daniel Tunkelang has a great post on this, where he found that one of his best questions was posted on Glassdoor.
Even for candidates that may know the answer in advance, they can still trip up on the explanation as to how the code works or how to improve it. Asking exploratory questions about their solution and how it could be extended is a good way to find out more of their thinking.