Pantech Link battery lasts about 3 hours of talk time and 10 hours on stand by. Texting is a bit more variable but should last around 5 to 7 hours of continuous use.
The pros of Pantech Link is that it's small, good keyboard, has 3G capability (though you probably won't use it as you stated). It has a 1.3 megapixel camera that takes decent pictures. Its back casing is rubberized for better grip so you don't accidentally drop it. It's very slim, so you can probably fit it in your form-fitting jeans without an embarrassing "is that your phone or are you just happy to see me" moment.
The con is that its screen is relatively small, especially in today's touch-screen age. But this is to be expected since it's a candy bar phone with a full keyboard. And its call quality can be improved, though not a deal breaker.
This phone came out in the earlier part of 2010, and should last you for about 2 years if all you do is text on it. Pantech phones are pretty reliable overall.
If you receive advice for getting a smartphone like Blackberry and Android-based phones, or even iPhone, beware that AT&T requires those phones to have a data plan at $20/mo or higher, and they've separated data plans from messaging plans so unlimited text will be extra on top of the $20/mo data. Pantech Link is considered just a "messaging phone" and so it only has the monthly requirement of $15+ messaging plan, or $15+ messaging/data combo (e.g. $5 for 200 messages, $10 for 200 mb data).