Alright well I have this problem too but mine is a little different from yours.
First of all if your INTERNET is disconnecting when you get a phone call then it's simple to fix. If you're using ADSL then it's probably a filter problem. You'll need to find out what your specific telco company recommends but for me I have the ADSL jacked straight into the wall without a filter. The I have every other device that uses the phone line (fax, telephone, security alarm) run through filters. These are very important, if your line isn't split correctly then your ADSL will disconnect whenever the phone rings because there isn't enough line left for it.
Now for the same problem on DIAL-UP, you simply have to find out what number to dial to disable call waiting. For me it's *52, so if I put that in front of the telephone number in my DIAL-UP it will disable call waiting while you are connected to the internet.
Now if your WIRELESS connection drops, when the phone rings it's usually because of this:
You have a cordless phone in your house that is using the same channel as your wireless router. Now routers are generally quite different so there's no one way to fix this. Just look up your make and model of modem on google and find out how to change the channel on your modem. It's pretty straight forward and not very time consuming to fix.
Also one thing to note is that you shouldn't automatically jump to the highest channel that you can because your wireless card may not be able to go that high.
If none of these work for you then let me know your specific problem and I will try to help as best I can.