Building something that has a patent and giving it away for free. Patent Infringement?

You can infringe a US patent by making, using, selling, offering to sell or importing into the US a product covered by the US patent. So, assuming what you would do would be covered by the patent, your use of the process would be an infringement.

At the risk of putting too fine a point on the matter, you simply have no idea if one or more patent claims cover the "service" that has captured your attention and which you now want to offer free to the public.

First, "services" are not patentable (only inventions are patentable) so I assume that you're referring to some nifty new process of doing something -- a "process" being, in quite limited circumstances, patentable.

Second, determining whether a patent covers an invention is a very fact intensive question. Many times companies receive patent protection for Invention X but they then offer a product to the marketplace or practice a method that is NOT covered by that patent. Their own product or method does not read on their own claims. It is not reasonable, or proper, due diligence to take a competitor's word on the scope of patent protection that it has on its technology.

Only a patent attorney can provide an opinion as to whether the process that you like is covered by whatever patent you've found. But going down that road is not fruitful. At the end of the day, you need to know if your process will infringe any patent that's out there. You need a "freedom to operate" opinion from a patent attorney -- especially now that you think a patent may cover the process you want to use.

Hire a registered patent attorney ( see < https://oedci.uspto.gov/OEDCI >) and talk through what you want you do and what you know is already out there. Good luck.