thanks @jjklee for the image!
Mike from Mobile Fanatics recently had the opportunity to talk with the Lumia 900 product manager. He specifically asked about the possibility to enable WI-FI tethering on the Lumia 900. Tethering allows you to share your internet connection wirelessly via WI-FI to other devices; basically your Lumia 900 becomes a WI-FI router that gives off internet to other devices. The good news is that it is totally possible. As you can see in the picture, you can easily turn WI-FI sharing on from the settings. The bad news is that it will cost more. This is not Nokia’s fault, it’s AT&T that has a policy to enable the “mobile hotspot” feature only on the DataPro 4GB plans, which run for $45 a month.