The Arlo cameras have their own WAP as I understand it so unless that WAP is somehow connected via Wi-fi to your router, it should represent a negligible impact. If you don't have a wired WAP, you're leaning on your Wi-fi pretty hard with up to five HD streams. Because Wi-fi bandwidth is shared amongst all active devices, the more devices, the more overhead there is in addition to the A/V streams themselves. A modern cordless phone shouldn't be a problem as they operate around 5.8GHz. Somewhat older phones live in the 2.4GHz band.