The official press release is as below:
Today, we've launched the SMS payment option for players from Denmark, Finland, Ireland, Norway and Sweden, which can be used to pay for a RuneScape membership.
RuneScape members will get regular content updates and gain access to a world that's three times larger than the free world and packed full of members-only quests, minigames and skills. Members also gain fullscreen mode, advert-free gaming and the ability to post on the forums. More information about membership can be found here.
The PayBySMS service is currently available to players from the UK, USA, Austria, Belgium, the Netherlands and Germany.