txting problem

[k_dizzle]

i just activated the xv6900 using the pay per KB plan, then i blocked internet data usage and download applications. now when i send txts over 20-40 characters people never recieve them. i never tried txting before establishing the blocks but im assuming thats the problem. does this phone use the internet connection to send txts? therefore using data? and could it be that sending a txt with more characters makes the txt to large and keeps the people im sending it to from recieving it?
any help is appreciated, thanks.