The primary advantage for both is that you can counsel with someone that is simply not available in your area. Some communities have no trained counselors, and telephone counseling is the only way to get help. But even in large metropolitan areas, it is sometimes difficult to find someone trained in a particular method that you trust.

Convenience is also a tremendous advantage. In terms of convenience, getting to and from a counseling office can sometimes take hours, which means the client might not be able to receive the support they need. Telephone and Skype counseling, on the other hand, can both be fit in more easily to a busy schedule.

How to determine which one is best for you?

Telephone Counseling 

Requirements:

A phone line 

A private place for you to talk

Advantages:

This may work best if you do not always have access to your computer,  or if your              computer is located in a part of your home or office where you do not have the privacy you will need. Additionally, sessions will not be interrupted by Internet connection problems. 

Appointment times and schedule changes can be more easily managed by both the client and the counselor as all that is needed is a telephone line and a private place to talk.

The telephone also affords you the privacy of not having to be "presentable" :-)

Disadvantages: Does not have the feel of Face-to-Face Counseling

Skype Counseling 

Requirements:

A stable Internet connection

A computer with a camera

A private place for you to talk

Advantages: In contrast to Telephone Counseling, Skype allows both the counselor and client a Face-to-Face counseling opportunity even from a distance.  

Disadvantages:

Last minute sessions or changes in appointment times may be more difficult to schedule as both the client and Counselor will need to have the necessary equipment to hold the session. There may be times when you need to change an appointment, or an issue arises where you need an appointment prior to your regularly scheduled meeting. Both the client and the Counselor may be able to find another suitable time to hold the session, but one or the other may not have the equipment available therefore making it impossible to hold the Skype session.

internet connections, as developed as they are, are more unreliable in terms of quality. Difficult Internet connections can interrupt sessions, and if reconnection is necessary, may take time away from your session.

Some clients prefer the privacy of the telephone as they can then hold the session without regard for their state of dress.