70 works for me too, find the html file and edit with notepad in your pc, I can access the one i have and post it if u have any trouble....
Here you go man:
Are there ways to enlarge the sms typing area?
you can use the freeware "TOTAL COMMANDER" and edit the file thread_sms.html. You can do a search to easily find it...windows directory.
look for this part:
<inbox:content id="COMPOSESUBECT" width="98%" height=35 spell...
and play around with the number in height (in this case 35). change to 70 and get 3 lines for text replies. Just change the numbers and see what works for you.
*you need to soft reset after editing the file.