Open rate is the share of delivered messages a recipient actually viewed. RCS can measure it through read receipts; SMS has no open event, so any SMS open rate is inferred, not measured.
Why SMS open rates are estimates
An SMS is a store-and-forward text with a delivery receipt at most. Nothing tells the sender whether the customer looked at it, so the widely quoted SMS open-rate figures come from surveys and extrapolation rather than from the network. Treat them as folklore unless the source explains how it counted.
What RCS reports instead
An RCS message from a verified RBM agent returns a read event when the conversation is opened, provided the recipient has read receipts on. That gives a genuine read rate per campaign. Two caveats keep it honest: recipients can disable read receipts, and messages that fell back to SMS report delivery only, so an open rate should be stated over the RCS-delivered portion and say so.
Reading it next to other metrics
Open rate says whether the message was seen; click-through rate says whether it prompted an action; conversion rate says whether the action was completed. SimplyRCS analytics show all three per campaign, split by RCS and SMS.