Hello not sure if this will help i found this online i have the cisco-9971 phone i put speed dial buttons my phone. Maybe this can help you too.
21
Pick up park 1
1
1
<line button="3">
<featureID>21</featureID>
<featureLabel>Pick up park 2</featureLabel>
<speedDialNumber>2</speedDialNumber>
<featureOptionMask>1</featureOptionMask>
</line>
<line button="4">
<featureID>21</featureID>
<featureLabel>Pick up park 3</featureLabel>
<speedDialNumber>3</speedDialNumber>
<featureOptionMask>1</featureOptionMask>
</line>
<line button="5">
<featureID>21</featureID>
<featureLabel>Pick up park 4</featureLabel>
<speedDialNumber>4</speedDialNumber>
<featureOptionMask>1</featureOptionMask>
</line>
<line button="6">
<featureID>21</featureID>
<featureLabel>Pick up park 5</featureLabel>
<speedDialNumber>5</speedDialNumber>
<featureOptionMask>1</featureOptionMask>
</line>
OK that wiki link was in regards to the intercom button. If you programmed intercom it would not actually work as in the background it does a speed dial. Please open a feature request at issues.freepbx.org to expose custom speed dial buttons for horizontal keys in EPM and we can get it added easy for you since our phone now supports it