Incoming calls while abroad

People calling you will still be able to call you normally.  WiFi Calling requires a compatible device and a reliable connection to work properly.  Calls made and received over WiFi Calling are treated like they are made and received in the US.  Make sure your device is compatible with T-Mobile's WiFi Calling implementation, make sure that your E911 address is setup on your account, and make sure WiFi Calling is enabled on your account.  

Sniper_Lion wrote:

I am going to India, but will need my mobile number to receive calls from the USA. I have a couple of questions - 

1. Will the person calling from the USA be able to call me normally, and will he/she be charged extra for the call?
2. If I receive the call, what would I be charged?
3. If I keep my phone on airplane mode and connect to wifi, will wifi calling work (wifi calling is free as far as I understand)?

I am on the ONE plan (family plan) without any add-ons as of now. 

First, what plan are you on? If you are on a prepaid plan, it is unlikely you'll be able to receive calls, and if you can, it will be very expensive.

If you are on a postpaid plan, see what @syaoran says but understand that roaming in India is very "messy". I think it has to do with the regional way that Indian wireless companies are licensed and organized. The result may be that you can roam a carrier perfectly well in, say, Gujarat but not get any service in J&K. There are many complaints about lack of service in India and the roaming map is not always a reliable guide.

T-Mobile’s info page for India.

Lista de control del roaming internacional

A word about WiFi Calling. Incoming calls are free. Outgoing calls are charged as if they were dialed from the USA. So, in my case, if I were to make a WiFi Call to India (from the US or from India) it would cost an outrageous $3/min. If I turn off WiFi in India and make a cellular call to an Indian number it's 25¢/min. Calls to US numbers over WiFi are also charged as if dialed from the US (e.g. free)

India is a place where I’d want to be really well aware of the details and have a backup plan.

Ssishikawa1 wrote:

I'm in Israel, can I receive calls for free?

Not cellular calls. WiFi Calls: Maybe. VoIP app calls: Yes.