It's possible to increase the number of call specifications records per report, the default is to show 10.000 records at maximum and it can be defined on on the following level (later has higher priority). 

Property levels

System level

To set in on the system level go to System Administration → Property management and set the following property to the number of maximum call specification records could be shown.

Reseller level

To set in on the system level go to System Administration → Resellers and open the reseller that should be configured. Set the following property to the number of maximum call specification records could be shown. Note that this value might already be set in the list, if so click Edit to  change the value for the property.

Customer level

To set in on the system level go to System Administration → Customers and open the customer that should be configured. Go to the Properties tab and add/edit the following property (KEY=VALUE) to the number of maixmum call specification records that could be shown. Go back to the Settings tab and click Save

reports.maximum_call_specification_records=10000

User level

To set in on the system level go to Administration → Users and open the user that should be configured. Go to the Properties tab and add/edit the following property (KEY=VALUE) to the number of maixmum call specification records that could be shown. Go back to the Settings tab and click Update

reports.maximum_call_specification_records=10000

Disclaimer

Due to performance reasons, the maximum call specification records feature is set up to 10000 records (incoming and outgoing summarized). You can adjust/increase this number to meet your requirements but it must be used wisely because increasing this number to a very high value might have a bad impact on the system performance,