This is not for the faint of heart, but maybe some hacker can turn this info into a quick-call applet. Here is the command line necessary to invoke click_to_call without opening the browser. Code: wget -O /dev/null -q --load-cookie=/home/user/.mozilla/microb/cookies.txt --referer=http://www.grandcentral.com/mobile/messages http://www.grandcentral.com/mobile/calls/click_to_call?destno=5185551212 So you must have already logged into grandcentral via the browser to make this work, and have previously installed wget through apt-get.
wget -O /dev/null -q --load-cookie=/home/user/.mozilla/microb/cookies.txt --referer=http://www.grandcentral.com/mobile/messages http://www.grandcentral.com/mobile/calls/click_to_call?destno=5185551212