To return the signed SS-4 back to LegalZoom, it could be mailed or faxed. This led down the path of researching online fax services, since I don't have a fax machine or combo-printer, nor did I want the added expense of another land line.
The following Internet fax service review sites were the basis of my decision to go with Faxage. Considering the minimal number of faxes anticipated to be sent or received, price was the ultimate deciding factor. $3.49 a month for a toll-free number to send and receive faxes!