Whether you've set up free digital downloads or you've sold digital files through the shopping cart, the files that your clients receive will be delivered via email. This email will have a link to download a Zip file of the images that your client requested. Since mobile devices like phones and tablets aren’t able to handle zip files, your clients will need to click the link in the email on a computer or laptop to be able to open the files.
However, if you have set up free digitals in a gallery, your clients will be able to download single images (one at a time) directly from the gallery. These individual files can be saved directly to a phone or tablet by following a series of prompts they'll see on-screen. (This is the only method of requesting a digital file that will not delivered via the email in a Zip file.)