Can I put my t-mobile sim card into an iphone?

I have an older phone. T-mobile is the service provider. I have a plan that gives me lots of texting and minutes with no data.

So can I buy an iphone (or maybe another smartphone) without the service, and then insert my t-mobile sim card into it and still get the texting and minutes, and also get wi-fi?

If it is unlocked you can. In a few months tmobile will sell iphones so if you use a tmobile iphone

You can, but not yourself! Bring it to the Apple Store to ask someone do that for you.

You can out the t-mobile SIM into iPhone if you satisfy the following two

1. Your iPhone is unlocked. Unlocked iPhones sell for whole lot more than with contract iPhones.iPhone5 unlocked starts at $649.
2. The SIM size matches with what is required by iPhone. Most older phones use a regular sized SIM. IPhone4 uses a micro SIM. IPhone 5 uses a nano SIM. A standard SIM can be cut to micro SIM by a cutter; local mobile shops/kiosks usually carry that cutter. Or you can buy a cutter yourself; they are inexpensive. See this video -
Or you can just order a micro SIM from t-Mobile. SIM cards per se are very inexpensive.
I am not sure if cutting is all that is required to make a std SIM into a nano SIM. The video referred to above suggests that cutting is all that is required.