The various Inmarsat FleetBroadband plans all do voice via VoIP. You can have a dedicated 64kb/s channel for voice, but you need the largest terminal (FB500) to be able to use it. VoIP works fine - there is latency, but since it's datagram
service via UDP, there's no need for fancy TCP spoofing like with e-mail and file transfers. If you're getting severe echo on a voice call because of latency, the cause is crappy VoIP
software on your PC/notebook/notepad, not the
service itself.
The top speeds you get are dictated by the terminal size. The FB150 (10" across) tops out at 150kbps, the FB250 (13") at 284kbps, and the FB500 (>24") gets up to 432kbps.
It's not the type of service you'd normally run a business on, but if you use the right setup and
software, it can be done. "Chatty" applications which handshake with the other end constantly will eat up bandwidth like you wouldn't believe. Webmail and other client-server apps are bad. Streaming video is worse. A smart e-mail client like Airmail is great because it's optimized for low bandwidth.
As twistedtree pointed out, HTTPS can be problematic because the encryption process (SSL - Secure Socket Layer, or TLS - Transport Layer Security) hides the data stream from the software process which "speeds" things up by spoofing TCP packet acknowledgments - the real speed killer in high-latency systems like geosynchronous satcoms). That's a whole other technical discussion beyond the
scope of this thread, but if you need speed and
security, there are devices called PEPs (performance enhancing proxies) which can speed things up dramatically. They are expensive, but if you're running a business then it's just a tax-deductible expense...