Telephone 
Telephone is a Telmex monopoly in the Ajijic, Lake Chapala area. It is usually reliable, but expensive for long-distance International calling.
Long Distance Calling

For long-distance communication, we recommend a Voice Over Internet Protocol (VOIP) service, such as Vonage. It's very reasonably priced ($29/month/unlimited calls). Some people also use a computer to computer service (i.e. Skype) which is free.
My clients are welcome to use the Vonage telephone in my office to call home when visiting here in Ajijic.
Public Fax Machines
There are several places where you can send and receive faxes to the US or Canada at about $1.50 US.
I am happy to provide this service for free from my office.
Internet Service
There are two Internet service providers -- Laguna and Prodigy. Dial-up, DSL High Speed and Wireless are all available options.

If you want to use the Internet only occasionally (for email, etc.), there are numerous Internet cafes in the area.
Most will help you set up an email address and give you some tutoring on its use.
Mail Services
Mexican mail is rather slow and can be unreliable. Typically, mail sent through the Mexican Postal Service arrives at a US or Canadian address in two weeks to one month, but there are numerous horror stories of four to six month delays ... or never.
Currently, there is a major effort to upgrade the Mexican postal system, including new uniforms, etc.
Probably the most popular option for sending and receiving mail in the Ajijic, Lake Chapala area is one of the commercial mail services (Mail Boxes, Etc. or Handy Mail). They courier the mail from here on a weekly basis to the US and Canada for $25 to $30 pesos per letter.
For receiving mail, they will set up a US address to which you can have mail sent, and then they ship it here to your private box at their facilities. This costs about $25 US dollars per month.
The Lake Chapala Society offers free courier services for members only, in which volunteers heading north take a bag of regular-size letters with postage affixed, and drop them in a mailbox after crossing the border. There are usually one or two volunteers per week.
Most of the major overnight services are available here, too ... including FedEx, UPS, and DHL.