When you're online, your dialup connection hangs up regularly. These are the common causes for this complaint:

• Someone else has picked up a phone, tried to send a fax, etc. 
• Other devices (phones, faxes etc) attached to the same line (somewhere in the house)
• Call waiting being enabled
• Your dialup provider may have an idle timeout
• Outlook Express may hang up after checking mail
• Line noise

Phone picked up: If your dialup connection uses the same line as telephones, a fax machine, security system, or dish tv box, you may want to consider getting a separate phone line for just your dialup connection. When you're online, if someone picks up a phone or tries to send a fax elsewhere in the home, your connection will often be dropped. Also, most security systems and satellite dish tv boxes connect to the phone line to transmit or receive data at various times, which can drop your connection. 

Other devices: Other phones and faxes can build up resistance on the line and cause a drop out after a few minutes. Disconnect all other devices and try again.

Call waiting: When call waiting is enabled, a tone can be heard on the line when there is an incoming call. This tone will disconnect your Internet connection, unless you first disable call waiting. Normally, this is done by dialing *70 before making a call. For example, if your dialup number is 555-1212, then you should change the dialup number to *70,555-1212. This example disables call waiting, the comma then pauses for a second or two before dialing. Check with your dialup provider on how to disable call waiting on a per-call basis in your specific area.

Idle Timeout: Many dialup providers have a 15-minute idle time out. If no data is transferred through your modem for a fifteen minute period of time, their modems will assume the connection has gone dead and will disconnect you. You will not be automatically disconnected from their system if you are downloading mail, actively browsing the web, or downloading a file. Check with your dialup provider to see if they have an idle timeout, and how long it is.

Outlook Express: Are you using Outlook Express on a Windows computer? Microsoft made the bad decision of making a single setting that disconnects your computer from the Internet default to On. Here's how to fix it. In Outlook Express, go to Tools and select Options. Click on the Connections tab. Make sure there is Not a check in Hang Up After Sending and Receiving box. Click OK.

Line Noise: There are two possible sources for line noise, they can be inside the home, or outside the home...

Line noise inside the home: Make sure that the phone cord from your modem goes directly to the wall. Splitters and devices designed to extend the length of your phone cord can cause line noise and result in lower connect speeds and frequent disconnects. Your phone line should not pass behind anything that creates a strong magnetic field, such as stereo speakers or a television (your monitor and computer speakers should be fine). Check to see if you have developed a bad phone cord between your computer and wall jack, have the line plugged into the wrong jack, or have someone there who is picking up an extension. Try plugging a normal phone into your computer jack, call a friend, then wiggle the cords around and see if you get disconnected or hear clicks, hissing, or popping noises. If you do, replace the phone cord. If after replacing the phone cord, you still get disconnected, hear hisses, crackles, and pops, you may have a bad phone jack, or bad phone wires in the walls, etc. If possible, try using a different phone jack to connect to the internet. You may need to have a phone company technician or electrician check the phone wiring within your home.

Line noise outside the home: There isn't much that can be done if the line noise is coming outside of your home, other than reporting it to the phone company. Often this kind of noise comes from bad weather or rain that may be affecting bad or exposed phone cables on the phone poles or in aging phone boxes. Also, if the local phone company's phone hub has too many simultaneous phone lines in use at once in your neighborhood, this can also cause poor modem connections and disconnects. Despite the source of the problem, phone company technicians will have to fix it, so report the problem to the phone company.