Internet prints at specified resolution (ppi setting)?

Is there any internet or mail order printing service that allows the
specification of a particular print resolution? I'd like to see how the
resultant print differs as an image is enlarged using resolution
upscaling, or instead enlarged by printing at a lower resolution.

For example, I'd like to take a 2048x1536 image and print at 200ppi
(8x10), but also also enlarge it to 3180x2400 and print at 300ppi (8x10).

Thanks,
-Mike