Just talked with Rakesh via olark (very helpful) on the Plivo site. I do a lot of stuff with Twilio and after talking with him, it sounds like Plivo has some valid strengths and advantages.
I am on of the founders of Plivo. Let me share with you what we think is different:
1. Native SIP Support. Works with any SIP Device. 2. Realtime Call Control (like in-call notifications etc..) 3. No Limit Conferencing 4. No carrier Lock-in 5. Volume pricing from the start
If you have any questions, feel free to ping us at support@plivo.com
Also, does plivo provide a softphone or client library?
Soft phone library is in roadmap.