i disagree, free texting apps do not hurt carrier profits for 2 reasons.
a) Users don't want another phone number, and even if they agreed, getting your friends to text you using that number instead of you carrier number is a large burden.
b)texts are priced so that even if you are able to use apps to cut down your texting, you don't save any money.
for example: a text costs 20 cents. verizon has a plan for 5 dollars a month for 250 texts. if after using apps you are able to get your incidental texts down to 25, you break even. Anymore and you loose money.
ATT is worse by forcing you into unlimited plans.
Which is why carriers are not afraid of iMessage. As long as users have a few incidental texts they'll still buy plans to prevent bill shock.
update:they mention point 2 at the end of the article but don't view it as damning as i do.