You may need to port your number to AT&T if T-Mobile's network does not have adequate coverage for you. That is one possible solution.
If you don't want to use AT&T and you want to stick with T-Mobile, you will probably need to port your number to Google Voice, activate a new T-Mobile SIM card, and associate your new T-Mobile number with your Google Voice account. After that, you can set up Groove IP to ring your Nexus 4 when you're inside your house. Groove IP will use your Google Voice number.
If Groove IP doesn't help, you can buy an "OBi110 Voice Service Bridge and VoIP Telephone Adapter" from Amazon for about $50. It's a box that you connect to your home internet and a regular landline phone. The OBi110 connects to your Google Voice account. When people call your Google Voice number, both your landline phone (using the OBi110) and your Nexus 4 (using T-Mobile) will ring if there is a good signal. If there is a poor T-Mobile signal, your Nexus 4 will not ring, but your landline phone will still ring because the OBi110 will route the call from the internet.
Please note that while there is no monthly charge for using the OBi110, you do not get 911 service. For that, you need to pay $12 per year. Also note that VoIP software (like Groove IP) is incompatible with the OBi110. I think they cancel each other out and nothing rings.
If neither Groove IP nor the OBi110 works for you, you may need to provide more details about your situation. We may need to resort to more complicated solutions.
Good luck!
I thought I was being clear.
First I wanted to know if porting my T Mobile phone number over to Google Voice would cancel my T Mobile service. Since it does, I don't want to do that as I would still like to make phone calls when I leave the house. Of course I could just get a new number from Google and use that instead but that would be a pain in the **** to tell everyone who wants to contact me to call this number instead of that number. How are they even going to know if I am home or not? My last question was, is there any other way to send and receive calls using wifi without having to use Google Voice or porting my current number?