RingCentral is a very sophisticated VoIP platform that you can use for your business telephony needs.
In the US and Canada, it also supports SMS and MMS messaging directly from within the app. In Australia, however, this is not available.
RingCentral users in Australia can use the IM features of the app with other RingCentral users, but not with standard mobile numbers.
BenkoPhone, however, does have the ability to send not only IM messages to other users in your organisation but SMS and MMS messages to any mobile number. It’s just like having a 2nd work phone, but in an app.