There's nothing magical about WhatsApp, it's nothing more than an instant messenger application on a mobile phone.
There's other proprietary, better compressed, (some) more secure, cheaper, and less intrusive apps with better security records and (some) less offensive privacy policies than WhatsApp on a whole assortment of supported phone platforms. There's also Nimbuzz, XMS, Fring, Viber, KakaoTalk, and Kik (amongst others) on the proprietary ends, and let's not forget about AOL Instant Messenger, Yahoo Instant Messenger, Google Talk and their accompanying applications as well as other various XMPP supporting applications like Talkonaut.
Kik has decent data compression (roughly 1000 SMS sized messages per MB), decent low-bandwidth push notification methods, minimal battery life impact, has only moderately invasive privacy policies, covers a fair number of mobile platforms, and doesn't cost a dime. Unfortunately, everyone's pretty well got some form or another of a spotty security record, so do keep that in mind on how you handle your username/password.
Whoever you choose, look into past security issues, read the privacy policy of the company providing the service, be sure the apps support the phone platform you and your buddies are both using, and you're both willing to use it.
Of course, if you actually went with Ting (IIRC), the prices for texting through them are dirt cheap already and if I were you, I personally wouldn't bother with texting alternatives unless others are rattling for it because they're trying to cut their bills down as well and aren't on Ting.