Help Will viber work w/ platinumtel intercept- how?

[e51]

I would like to use use VoIP with a pay as you go plan.
Platinumtel (Sprint) offers the Samsung intercept, 2,1. Has anyone used Viber with their Intercept and with Platinumtel? What has been your experience?

Are there any other ways or service to do this?

Your thoughts / advice will be appreciated.