CDMA Phone service vs 3G service – Seperate?

I have two accounts on Sprint – The first with unlimited voice and text, but no data, and another with unlimited Internet service, but very costly voice and text charges.

As far as I know, it is possible to put both on one flashed phone, but I’m not entirely sure.

I seem to recall something about EVDO only using some EVDO-specific parameters to authenticate…

So, can it be done, in such a way that phone calls, texts, and data all work seamlessly without some kind of clumsy switching hack?

If I’ve posted this in the wrong section, please let me know.