WhatsApp vs SMS Marketing: Which One Wins for Cold Leads

You've got a database of contacts that have gone quiet for months, and you need to decide what to wake them up with. SMS or WhatsApp? The short answer is that it depends on three things: how cold the contact actually is, what you captured at the point of opt-in, and how much you care about getting a conversation instead of a flat notification. The long answer means looking at real numbers, real rules, and real costs. Choosing wrong doesn't just waste budget — it risks complaints, sender-number blocks, and contacts burned for good.

In this guide we put the two channels head to head on the specific ground of reactivation, meaning the contact isn't expecting you and isn't warm. And we give you a decision matrix by industry, so you don't have to guess.

SMS and WhatsApp don't do the same job

The first mistake is treating them as interchangeable channels. They're not. They answer to two different logics.

SMS is a car horn. It arrives, it gets read (the open rate for SMS is above 98%, and in most cases it's read within minutes), it doesn't require the recipient to have a specific app or to have ever written to you. It works on any phone. And it's one-directional by nature: you send a message, the contact clicks a link or does nothing. Perfect for a sharp nudge with a clear call to action.

WhatsApp is a conversation. It lands in the app the average person opens dozens of times a day, it supports images, buttons, catalogs, automated replies, and above all, two-way exchange. The contact can reply, you can qualify them, book an appointment, handle objections. But WhatsApp Business has one iron rule: to start a conversation with a cold contact you must use a template pre-approved by Meta, and that changes the whole game for reactivation.

The difference that matters most: who can message first

With SMS you can contact anyone who's given you consent, whenever you want. With WhatsApp, for a contact outside the 24-hour window (meaning anyone who hasn't messaged you in over a day, which is exactly the case with a dormant contact) you can only reach out with an approved Message Template. Meta reviews them, can reject them if they're too promotional or poorly built, and assigns a quality rating to your number. If too many users block or report your templates, Meta lowers your sending tier and, in serious cases, suspends the number. That's not a minor detail — it's the constraint that determines how you can actually use WhatsApp on cold contacts.

Head-to-head comparison on cold contacts

A note on costs: the figures reflect the Italian market in 2026 and should be verified with your provider, since Meta has repeatedly revised WhatsApp's pricing model (from per-conversation to per-message for some categories). The substance doesn't change: SMS costs less per touch, WhatsApp costs more but buys you a conversation, not a notification.

When to choose SMS

SMS wins when reactivation is an impulse move and the conversion happens elsewhere (a landing page, your site, an online booking). Choose it when:

• You only have the phone number and no certainty the contact uses WhatsApp or has ever interacted with you on that channel.
• The message is a simple impulse: a win-back discount, a reminder about an expired subscription, a deadline. Something like: "Still with us? Your 15% off is waiting until Sunday, [link]".
• The contact base is very large and the cost per touch has to stay rock-bottom for the ROI math on a broadcast to work.
• The audience is less digital-native: age groups or industries where SMS remains the most reliable, least filtered channel.

SMS on dormant contacts can reach a triple-digit ROI precisely because the cost per contact is negligible compared to acquisition: reactivating a contact costs 5-7 times less than acquiring a new one. The limit is that it stops there: if the contact doesn't click, there's no second act. And if you hammer too often, SMS becomes the most hated channel and complaints climb.

When to choose WhatsApp

WhatsApp wins when reactivation needs to become a conversation, not a click. Choose it when:

• The customer's value is high and it's worth investing in an exchange that qualifies them and brings them back to an appointment (services, B2B, real estate, private healthcare).
• You need to handle objections or book something: a template that opens the door, followed by a conversational flow that leads to setting a date. This is where automating WhatsApp Business with AI makes the difference between replying in 2 seconds and losing the contact.
• The message needs visual richness: showing the product, a catalog, quick-choice buttons.
• You want a channel the contact experiences as direct, not as mass advertising — provided the template is well written and states upfront who you are and why you're writing.

The flip side is Meta's constraint. Every template has to pass approval, every user report weighs on your number, and the coldness of the contact makes it more likely someone replies "who is this?" or blocks you. You need a clean opt-in and a credible reason to reopen the conversation, not a promotional blast in disguise.

The factor that really decides it: compliance and consent

This is where ninety percent of badly run campaigns fall apart. Reactivation isn't a free-for-all: you're contacting people who gave you their data months or years ago. Under GDPR, consent isn't eternal, and it has to be managed.

Two operating principles worth keeping in mind (informational, not legal advice):

• The consent validity window. EDPB guidance and Italian Data Protection Authority (Garante Privacy) practice converge on a reasonableness window of around 24 months of inactivity, beyond which an old consent becomes hard to defend. Cold-contacting someone who hasn't heard from you in three years is slippery ground. Dig into it before you start, in the guide on how to reactivate old customers in compliance with GDPR.
• The legal basis. Explicit consent or documented legitimate interest: without one of the two, both SMS and WhatsApp are exposed to penalties, no matter how good the copy is.

WhatsApp adds a layer: Meta requires a channel-specific opt-in. Having the email and phone number isn't enough. If consent doesn't cover WhatsApp, the template might technically get approved but you're still exposed. SMS is more permissive on the technical side, but not on the legal one: GDPR rules apply just the same.