Both channels work. The question is which works better for your specific customer relationship, and whether combining them is worth the effort.
SMS: higher open rates, faster action
Text messages have open rates above 90%, compared to around 20-30% for email. Most texts are read within 3 minutes of delivery. For a review request, that means a customer sees your message while the experience is still fresh — which is exactly when they are most likely to act. The downside is that SMS feels intrusive to some customers if you do not have an established relationship, and some industries have stricter compliance requirements around text messages.
Email: more control, works for complex messages
Email allows more context and formatting. You can include the customer's name, reference their specific service, and give clearer instructions with a button. Email also reaches customers who prefer not to share their phone number. Response rates are lower than SMS, but email review requests still outperform no follow-up at all by a wide margin.
The combination approach
The highest-performing review collection systems send an email first, then a short SMS follow-up 3 to 5 days later. The email sets context and the text converts. Customers who respond to the email never get the text. This approach captures both the fast responders and the people who need a second nudge.
Which to start with
If you have customer phone numbers, start with SMS — the faster results are motivating and the setup is simpler. Add email as a second channel once the SMS process is running smoothly.
Compliance note: Always get explicit consent before sending marketing SMS messages. Use an opt-in at the point of service or purchase. Review request messages may qualify for transactional treatment in some jurisdictions, but consult the rules for your region.