Our intention is to make things as simple as possible for the client. We can upsize your images for you (within limits), or you can send full sized images at 300 dpi and we will take it from there.
When choosing a digital camera, generally the more resolution, the better. If your original file size is 2 MB or larger, it probably will be just fine. If you are a purist, send us the full sized image.
Cell phone cameras usually take poor photographs, but even then we surprise ourselves how well they can turn out.