you'd probably just have to bite the bullet and get a unlocked one like this:
http://www.amazon.com/HTC-Unlocked-S.../dp/B002C2S272
though an at&t or tmobile version might have what you need too.
edit, this is all I could find on it:
Phone: CDMA dual band digital phone with EVDO Rev. A and 1xRTT for data. Also has a SIM card slot for GSM quad band world roaming 850/900/1800/1900MHz bands with EDGE and 2100MHz 3G HSDPA for Europe and Asia. The SIM slot is unlocked for use with any GSM carrier but the phone doesn't work in the US with American GSM carriers (e.g. T-Mobile and AT&T).
looks like if sun cellular's 3g is gonna be on 2100mhz, then you'll get 3g, otherwise, you'll get edge.