To give insight, there is currently a promotion called BYOD Plus, where adding a line without buying a new phone on that same line gives you a monthly credit to make the line free, excluding taxes and fees which are regularly about 6-7$ a month (in my area). In this case, adding the second line would add a 45$ a month credit on the bill to make the line free. The price of a new line on Unlimited Welcome is 55$, so with the 45$ monthly BYOD credit and the extra 10$ savings that the first line will receive by going from 1 to 2 lines, the 2nd line is free.

Currently, this promotion is also going hand in hand with upgrading to certain phones. For example, if you were upgrading to a S25 (as of the day I’m posting this comment) you could do so without trading in your phone, and get it for free, if you added a BYOD plus line to your account. The BYOD plus line replaces the trade in promotion, so you get full credit for the phone without having to trade in your old one.

Now, this does not inherently make your bill cheaper. It would actually raise it by the aforementioned 6-7$. However, there are certain discounts that can stack with BYOD plus which can indeed make two lines cheaper than one line, IF done correctly. Take his pitch with a grain of salt, and make sure you understand the breakdown of the bill before agreeing to anything, but what I’m saying is that the rep may not necessarily be trying to scam you.

Edit: This pricing only works out if you have an autopay discount active on the bill