The Device Filter on the Akixi reports has a default limit of 150 items. If your customer has more than this, only the first 150 will be shown. This list includes all devices, e.g. extensions, hunt groups, voicemail devices...etc
To increase the number of devices shown, modify the report and click on the "Advanced" tab. In the Content Restriction section, change the value in the "Maximum Filter List Limit" box to a suitable value. The maximum value for this is 4000. It is recommended to keep it relatively low to improve browser performance.
Note that if you change the report style or date/time settings, this value will be reset to 150.