they blocked it because lots of people started to use viber and other VoIP services to make calls instead of making calls which reduced alfa and touch profit,specially with almost everybody with a smartphone having a 3G subscription these days.
Whatsapp might get blocked but i don't see it coming since lots of people use 3G just for whatsapp,so 3G subscription will cover the loss in SMS traffic.
as for a having a workaround it's fairly easy,just use an VPN service to bypass the block,a good VPN with unlimited bandwidth is
Hotspot Shield (it's ad supported but rooted users can easily block ads),another great apps which also compresses traffic is
Viatun.