Which T-Mobile phone should i get? The Samsung Gravity or Samsung T639?

I love flip phones, with the ability to hang up and pen to answer a call. But i have the option of a slide phone, aka the Gravity, with its obvious extra abilities, plus the keyboard option. I don't have a texting plan yet, and i'm not sure if i'll receive one, so if i get the Gravity i might be at a disadvantage, especially with its button pressing in order to answer the phone

What are your opinions? Which would you recommend and/or what are your thought about these phones and my situation indvidually?