My personal recommendation for mobile Internet in Finland, is to use a Prepaid 3G/LTE Data Sim Card:
The Prepaid Sim Card including 10GB Data valid for one month is about 20 Euro.
Curiously you cannot buy the Sim Card in a Sonera store, but they sell them at newspaper stands like R-Kioski (www.r-kioski.fi).
Mobile Internet in Finland – going online while travelling – using a USB-Stick / USB-Dongle or a mobile Wifi hotspot (Mifi) together with a local Prepaid 3G/LTE Data Sim is, thanks to decreasing prices, super popular like never before.
If you need access to the internet while on vacation or during a business trip in Finland, a Prepaid Data Sim Card from a local provider is a good choice. This way you are bypassing the super expensive International Roaming fees of your provider at home and you have access to much larger data packages at an extremely low price.
Using a Prepaid also known as, Pay as you go service, abroad you don’t have to pay a monthly fee. Normally you pay a fixed amount upfront and therefore get a certain volume of data (GB) that you can use for a specified period of time.
To speak from my own experience, I can absolutely recommend using a mobile Wifi hotspot, also known as Mifi. Using you Smartphone (Tethering) is also possible but, you will run out of battery very fast. Another advantage of the Mifi over your Smartphone is the fact that you can leave your domestic sim card in your phone, which enables you to also keep your cell phone number.
The Mifi devices are often pocket-size and smaller than a smartphone. The battery will last between 4 to 6 hours. How they work, they start a Wifi Network and all devices, like Smartphones, Laptops, Tablets, etc. can go online at the same time using this Wifi Network. Depending on the Mifi model and your mobile network connection, you will get 3G or even very fast LTE speed.