Simplify the following text for a Grade 4 native English-speaking person.
Original: By this time , the ISM bands had become crowded in the U.S. , especially the 2.4 GHz band which is used by both the most common variants of Wi-Fi , 802.11 b and 802.11 g , and many cordless phones ; thus interference between unlicensed devices has become common in these bands . However , because Wi-Fi does not operate in the UPCS band and DECT devices negotiate with each other for the available spectrum , not only are DECT 6.0 phones immune from this type of interference , their operation does not impair other nearby devices operating on the same frequency , which is a common issue with 2.4 GHz cordless phones .
Simplified: As DECT 6.0 does not operate in the 2.4 GHz ISM band , it is not subject to the interference arising in this band from its use by 802.11 b and 802.11 g WiFi , and 2.4 GHz cordless phones .