Like DrDave said, it is not possible with a HDMI port. That port would be used to pass video and audio to a device with a HDMI input such as a newer TV.
There are several options however, If you already have a mobile broadband dongle, there are special wireless routers that accept USB dongles.
What I personally use for my laptop and tablet when I'm away from home is a cellular wireless mobile hotspot app on my Verizon smartphone.
It acts like a mini wireless router, you just turn it on the phone and can connect up to 5 wireless devices such as iPads, laptops, etc.
You'll have to pay for a mobile data plan from your cellular provider.
Be forewarned that most have low monthly data limits and buying more is expensive, so you wouldn't want to use it to stream a lot of Netflix movies or try and replace your home DSL or cable Internet service.
I have a 6 GB shared family data plan and find that more than adequate, you'll have to monitor your mobile usage for a few months and upgrade or downgrade your data plan to match your usage.
If you don't have a smartphone with wireless mobile hotspot capabilities you can get a separate portable mobile hotspot device such as the MiFi from your cellular provider. This will cost a little more because the device needs it's own account and number.
Good Luck...