Wanted to get this straight…
ReadyLink is a $15 plan addon (per line). If you have Vision, you will have to remove it and add the ReadyLink+Vision plan addon which is $20/line. If you’re getting Vision for free, or have Unlimited Vision, or have free Vision on shared lines, you will have to drop it in order to add ReadyLink.
Sprint also has a ReadyLink-only plan for $45 a month, which has no voice calling, but unlimited ReadyLink. Vision can be added for $10 more.
The ReadyLink+Vision addon is similar to the older Unlimited Vision (no download credits), but it lacks Picture Mail, so you will have to add that on for an additional $5.