What FINS said!
Phones and tablets are the weak point of many WiFi systems, but the 'marketing icon' at the top of the customers screen will tell them that everything is fine at their end. When in reality, the issue is that the phone or tablet is happily receiving data, but is simply unable to communicate and send the info back to the Access Point due to tiny little antennas that are designed to fit in a phone... next to a battery... and be transported in your pocket or bag!