With Handcent you can adjust your font size in Settings-> Custom Style-> Bubble settings, then adjust your incoming and outgoing font including size
I did try Handcent, which was okay but i just wanted an app that enabled you to alter the size of text in the stock SMS application and box above the stock keyboard. My wife has a Nokia 3110 and is able to adjust the text size on her phone.
Why can't Samsung/Google appreciate that not everyone has 20/20 vision?
Okay I might wear reading glasses to read a newspaper/book, but if I am on the go walking and get a message I want to be able to open the message and read it/respond to it without having to dig my reading glasses out my pocket first!
I did install 'ThickButtons' which helped with typing, but I can't believe Android developers can not emulate Nokia by including a text size adjustment as standard, to help us 'visually challenged' people!