Solution: This problem can be caused by a number of issues. Here are some of the most common causes, and some solutions.

1. GTE Voicemail (called "Personal Secretary"); This service acts as an answering machine, without the machine. But instead of a blinking light to let you know that you have a message waiting for you, you now have what is called a "stutter tone". When you pick up the phone, instead of having a clear dialtone, you have a series of broken dialtones that lasts for about 2 seconds. This stutter tone is enough to confuse the computer into thinking that there is no dialtone on the line, and so it just gives up and returns an error that it could not detect a dialtone. The solution to this is to check your phone messages, and then try to go back online. This will clear the stutter tone, thereby making it possible for the computer to dial out.
2. The phone cord is plugged into the wrong jack; This is a common problem when people are just setting up a new computer, or have moved their old computer to a new phone line and the phone cord gets plugged back into the wrong jack. On most modems, there are two jacks in which a phone cord can be plugged in (note: the exception to this is a Macintosh running an internal modem; there is only one jack on the back of the computer. This does not apply to Macintosh computers running an external modem). One of the jacks is typically labeled "Phone", and this can be confusing. The cord coming from the wall jack should NOT be plugged into the jack on the modem that is labeled "Phone". Instead, it should be plugged into the jack on the modem marked "Line" or "Wall". The jack marked "Phone" is there so that a telephone can be plugged into the modem; this way, the computer and the phone can be plugged into the same phone jack without the use of a line splitter; the computer is plugged into the wall, and the phone is plugged into the computer.
3. Modem damage caused by lightning; Invariably, our tech support desk will get at least one call a day or two after a major thunderstorm claiming that a modem is no longer able to detect a dialtone. Lightning storms can damage computer modems, even without a direct lightning strike. A simple static discharge on the phone line can fry a modem, leaving the computer itself intact. For this reason, we always recommend that if there is a thunderstorm looming on the horizon to unplug not only the computer from the power, but also to unplug the phone cord from the computer. This way, there is no way that lightning can get to your computer.