Kellogg Telephone

I have a Kellogg Switchboard wall phone that was my great grandmother's on her farm in Colorado. Based on some research, I believe the phone was manufactured in 1929 but wanted to see if anyone knew for sure. Last inspected date lists March of 1929, although the year is hard to make out for sure. It is a 5-bar set which would make sense given that the phone was on a farm. There also may be a secret calling button which is located on the left side of the phone. Thanks for any other helpful information!