For a few years now past students of mine have requested correspondence lessons since I relocated 250 miles away from the suburbs of Boston.  Nothing is better than working with a teacher face to face in any instructional situation, but if you found a teacher you really like and "click" with and their schedule is full, if your unable to find a competent guitar instructor in the immediate area you live in, live in a rather remote area and are unable to attend one-on-one lessons with a private instructor on a regular basis or maintain a difficult schedule due to work, family, etc.  Then correspondence lessons are the way to go.  Many students learn to excel through this method of teaching and many accomplished musicians learn to play better.
If you are a total beginner (attending lessons less than 6 months) than I highly recommend against taking correspondence lessons.  You should seek professional private 1 one 1 instruction in your area.
How correspondence lessons work:
Lesson assignments:
For those of you who are new students of mine, lessons are written in notation & tab with software that is used by all professional publishing companies.  From time to time a question asked might stray off the basic subject and I may have to hand write notation and/or tab for the personal lesson.  Over the past 16 years of professionally teaching I have accumulated an amazing amount of lesson sheets so everything is progressively organized and meticulously neat.
Audio CDs:
At times lessons are accompanied by audio CDs made specifically designed for the lesson.  Audio CDs cover many subjects.  In the question following a student asked me about some measures of music he suspected to be transcribed incorrectly in the sheet music he bought.
CD's of the song material studied are made so the student can practice along with music at different speeds (while maintaining the pitch of the music) 1/2 speed usually to start with and then increasing tempo by 5-percent each track until the original  tempo is reached.
I transcribed the measures in question and sent him both a practice CD and the music.  Then posted the information on my site for him to access immediately.  Q&A Joe Satriani solo example.
Subjects Studied:
Music Theory                                 Ear Training
Composition                                  Improvisation
Exercises                                    Technique Studies 
Sight Reading                                Scales & Arpeggios
             And there applications in music.                     
When you sign on as a correspondence student a 1/2-hour time slot is reserved for us to...well correspond about the lessons previously sent to your home address.  4 lessons are assigned per month and are dated to be done weekly.
I meet with students on the same day at the same time once a week to go over the lesson and answer any questions.  For example every Monday night at 9:00 pm I meet with Jeff.  It is the same scheduling system as private 1 on 1 lessons you would attend at a music store or private music school.  Currently communication has been done through messenger.  If you have questions during the week e-mailing me is perfectly fine as long as the number of e-mails is within reason...
(Very funny Jeff with the 300 e-mails)  Lesson cost is $100 per month to be paid in advance before the lessons of each month.  Most students send payment the last lesson day of each month as to not miss the month.
  I work with too many students to keep track of them all any other way than month to month.  If you have taken professional lessons before than this is no different than the tuition system used by music stores and schools.
After signing up and working out a scheduled time you can print off the
information form or I can send it via e-mail.  This is so I can get insight on your level of playing, personal goals, etc. than I can set up a personal practice routing to help you reach your potentials. (Students I have worked with in the past should also fill out this form).  I am sure you have grown & learned many things since we studied together.  Send back the Info form back to my residence with payment and in a couple of days the lessons should hit your mailbox.
If there are no time slots at the time of your inquiry students are put on a waiting list and signed on in the order of which I receive requests.
* Any inquiring student I have worked with in the past or at present through any music store or school are not eligible for correspondence lessons.  This is a breech of contract. 
To sign on as a correspondence student please E-Mail me.