It does happen but it is within the specifications set for cell phones. You can't avoid it as it by design is a radio transmitter and has to be to be able to talk to the Whispernet network. All cell phones will do it as it is a side effect of how they operate.
I'll spare you the details of why exactly it sounds like that though.
If you turn off wireless then you won't get the cell phone interference. If you buy a WiFi only Kindle then you won't get this interference even with wireless enabled as it won't have the cell modem inside it.
There currently isn't any method of enabling only a specific type of wireless. Its all or nothing currently.