You have to enable call swapping.
-<param name="enable-analog-option" value="call-swap"/>
Add that to the <settings> section of your freetdm.conf.xml
Moises Silva
Senior Software Engineer
Sangoma Technologies Inc. | NEW 100 Renfrew Drive, Suite 100, Markham ON L3R 9R6 Canada
t. 1 905 474 1990 x128 | e.
moy@sangoma.com