SMS is a thing of the past especially when you travel overseas allot. I was surprised when ATT charged me 25 cents a text both send and receive when i went to Canada on business even though i had their overpriced $15 for 1500 texts a month. Appearently Canada is international and you need an overpriced international texting plan.
After i got that bill for over $100 i said F that, removed both my text plan and my data plan from my smart phone and installed Whatsapp. I have wifi at home, work and optimum wifi when i walk around in the city. My bill dropped from $80 to less than $50 a month and thats with 20 cents pay per texts and i only text about 20 times a month max which equalls about $4 pay per text. Everything else is through Whatsapp which i will gladly pay the $1 per year for. And this is on a 2 year contract.
Whatsapp is cross platform.
BBM and iMessage are late to the race and the only people who still use it are people who do not know they have a choice to install and use something else.
I used to have Android, but as a software developer I found that most of the apps I downloaded from the google PlayStore where doing something nasty in the background. It's not going to change all the while Google takes an unvetted approach to the PlayStore.