I have not tested it, but check this api: http://code.google.com/p/google-voice-java/
In particular, voice.java on line 711 , which is a method:
public String call(String originNumber, String destinationNumber, String phoneType) throws IOException {
On line 737 they use:
URL callURL = new URL("https://www.google.com/voice/call/connect/");
and full comments on the methods say:
// POST /voice/call/connect/ // outgoingNumber=[number to call] // &forwardingNumber=[forwarding number] // &subscriberNumber=undefined // &phoneType=[phone type from google] // &remember=0 // &_rnr_se=[pull from page]
Hope this helps.
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