If you go with a laptop, you will only be able to check your internet and access the web at places that have free wireless internet (Panera bread, Kansas City airport, etc.) without buying a special card and paying a phone service to provide you with internet. Best I can tell, this will cost you at least $20/month.
If all you need to do is access the email and internet, you don't necessarily need all the functionality of a laptop and a phone device might be the best way to go, especially if you're already paying for a cell phone (in which case it's just a little more a month than you were already paying) or are in need of a cell phone! I *highly* recommend the G1 if you're with TMobile and the iPhone if you're with AT&T. The amount and variety of applications you can put on them is amazing, from movie times tailored automatically to your location, calorie trackers, aids to help you find where you parked your car (the phones have built-in GPS and have helped me find my way from one place to another a million times), shopping lists, barcode scanners that quickly tell you the lowest prices that can be found for that item, a flashlight, and so many more you can't even imagine-- all at the convenient touch of a hand!
Having read the other responses let me add that neither the iPhone nor G1 have screens that are too small too use. Both make it very easy increase the size of anything on the screen to whatever size you desire. They both use "full" internet, too, the same as you'd have on a laptop, on either wireless internet speed, the 3G network (nearly as fast as wireless), or 2G network (which is more like dial-up). The iPhone has top-notch support as well via your local Apple store, online support site, and phone tech support.