Will my unlocked T-mobile dash work outside USA?

You can use your unlocked T company mobile in India.

The other thing is that if your mobile is unlocked than you can use it in any part of world.

Also you can use all features of your mobile with your unlocked any company mobile.

If you come India for lesser days than if your sim card company provides international roaming than without changing your sim card you can make and receive call. But it will be too costly. But any one from USA can also call you on same number.

If you come India than you can immediately buy SIM card. For this a passport size photo and xerox of passport will be needed. SIM card activation may can time up to half an hour. Also call rates in India are much cheaper and 3G is also available in major cities.