I have Verizon Fios High Speed intenet service and connect wirelessly through either a Gateway, IBM or MAC laptop. If the phone rings while I'm online, the internet service goes down while on the IBM or the Gateway; the MAC is never disconnected. What could be wrong?
That means you have cordless phones, and those cordless phones are on 2.4Ghz. Which is the same frequency as the wireless internet.
The only permeate solution is to replace the phones with a different frequency.
However some have had luck by changing the wireless channel on the internet to channel 11. This is NOT a solution but it can help reduce the problem. You log into the router (192.168.1.1 username = admin password = password or password1) go to the wireless settings, click on "basic settings" and change the channel from "auto" to channel 11 and click save at the bottom. This does not solve the underlying problem of having two devices on the same frequency but it can get them onto different channels so that the interference is reduced. But it is not eliminated altogether.
Spacedebris is right about the cordless phone probably being the cause. However, my experience is that changing to Channel 1 worked best. I tried 11, didn't help in my house, but channel 1 did. So I suggest you try 11, maybe then 1, then others, and hopefully you will find one that helps. And at least for me, I have never ever had a loss of wireless connection using Channel 1 when the cordless phone is in use, and the wireless phone base is about 3 feet from my wireless router (with two remote wireless phones using that base, and my wife is on the phone a LOT!).
Basically, just don't give up if one channel doesn't work, try them all, 1 - 11. But if none work, then a change to a non-2.4GHz phone is probably the only solution.