Between Verizon offering unlimited text messages and Apple's iMessage, I'm just not seeing the need for this app on my phone.
I actually resisted installing WhatsApp for a long time (over a year) because I didn't see the need or reason why so many people were excited about it. To me, it didn't feel like "native texting", so what was the point. But I was wrong. It's a really well-built, clean app with great texting, audio, video and picure support, and for me it provides the cross-platform support and international (Canada <-> Singapore) texting that I need. No way I could get that from a carrier's own texting service. iMessage is an option for me, but between my phone and an iPad, not another phone, at this time.