First of all, you will need a voip account or google voice to use your OBi in this way.
Secondly, if your home phone number is provided by your local Telco on a standard landline then there is a way to do this. Get a phone number you can point to your voip or google voice account and then forward the calls from your landline to it.
If your home phone number is already pointing to your OBi then just plug it in to the internet wherever you are and it should work.
If you can expand your information a bit further we can give you a more definitive answer.