Hello g227z82w, I don't know if I can help you with free on the mailbox number, but I can help you with inexpensive.
Mailboxes and Postal ServicesAgain, the free option is to just use your current one. Which is perfectly fine and legal. I'd let your mailperson know if you all of a sudden plan getting mail to your business name.
For outgoing packages, you can now get free pickup from all the major carriers at your home, even the US Postal service. With the new Click-N-Ship at USPS.gov, you can print and pay for postage online, and request a next-day pickup. Spending $20 on a scale keeps you from overpaying for postage, and probably saved me that much in gas alone.
If you are looking to create a virtual office, you can try magicjack plus or the original magic jack for phone service, and yahoo and gmail for email addressess, as well as efax.com for fax number. These are all very inexpensive.
Hope this helps.