This always happens when you call your own number from your number. There is a solution, but will require an extra step, and account. I do this with my service since I have Google Voice for Android on my cell phone, and my home phone uses an Obi100 with GTalk.
Step 1: Go to CallCentric. I am suggesting CallCentric as they will provide you with a free US (most likely NY) telephone number. Create an account, and get a free US Number.
Step 2: You will also likely have to pay for E911 service which is about $2.00/month. Be prepared to whip out the credit car. This is CallCentric's requirement anytime you can make a call, or receive a call as well as being in the US/Canada.
Step 3: Set up your CallCentric account up on the second line. It may take a couple of minutes once you entered the credentials.
Make a note of your new phone number from CallCentric. When you need to call home, you simply call the CallCentric Number. I am sure there is a way to set up ObiHai to automatically call your Google Voice number using the CallCentric line from home, but I don't know how since I only had the box for about a day.
Hope it helps,
Frank