Runescape members can currently test Runescape Mobile, but that membership costs real money.
However, you can bypass this by grabbing the current giveaway on Twitch Prime.
This offers you a free month of Runescape membership, including Old School and the new and improved versions.
Check out Runescape Mobile early with Twitch Prime
Once you’ve redeemed the giveaway, you can download and check out Runescape Mobile for a month. This is limited to just Old School right now though, so bear that in mind.
Twitch Prime is included with an Amazon Prime subscription, which does cost real money. However, you can get a free trial and redeem the giveaway that way.