It's very easy, I and some of my friends done it, just pick a DR shipper convenient for you and keep it under $200 so no tax applies (make sure main seller has free shipping within US or the $200 should be inclusive of the main seller's shipping cost). As far as I know....
You ask the main seller to ship to the DR shipper US address and then they take it over from there and deliver it to you (or their office in DR).
Ah, very important, make sure the cellphone is 100% unlocked from any US company or it won't work in DR.