The biggest mobile billing casinos are Boku and Payforit. Payforit is a payment solution created in a joint effort by Virgin, Vodafone, Three, O2, and EE UK mobile carriers. Boku, on the other hand, is an independent payments provider. The Nordic mobile billing services Siru Mobile and Zimpler aren't available in the UK yet; however, Fonix is slowly creeping into the casino market.