As others have stated, if you have no listings and the brokerage allows it, you may want to but why bother with an open listing at all? Why commit to a listing where the owner has not committed to you? As someone else stated, get training from your brokerage to obtain your own exclusive listings. That's where it's at. The brokerage community will be calling to show it to their buyers and that's the best position to be in. Good luck.
As mentioned below, each firm has their own policy about open listings. If it is allowed by your company, you can do it if the seller wants you to. Make sure you have a commission agreement in place as well, as you will be entitled to a buyer side commission if you sell it. Bear in mind though that if you are putting it up as an open listing, several other agents may too and it will look odd that a few of you are advertising the same property. It will also feed into OLR and RealPlus, and you will get a lot of other agents calling you and you will have to explain that you cannot co-broker it, which will not be received well.
should have a data base with open listing and exclusives as well so you don't have to call agents and brokers who advertise open listings ( they will not co-broke and must likely will not be cooperative with information).
In short I agree with Anna.