You don't get a Boku account, per se. As mentioned above, Boku is great because you don't actually need a special account on top of your already established accounts so no extra passwords or usernames are required.
All you need to use Boku as a poker deposit method is a mobile phone number with a carrier that is connected to the Boku service. Dozens of major carriers across most major countries have Boku services. To see if your carrier is one of them, check with your local services provider.