Pick Postscript if SMS is the main channel and you want published plan tiers plus per-message rates you can model. Pick Klaviyo if you want SMS sitting on the same customer data and flows as email, with a listed monthly SMS plan that includes carrier fees. Pick Attentive if you want SMS, email, RCS and push in one platform with a dedicated support team, and you are willing to work from a quote. Pick Omnisend if you want a free plan to start and are happy adding SMS per message on top of an email plan.
At a glance
 Attentive |  Postscript |  Klaviyo |  Omnisend | |
|---|---|---|---|---|
| Built for | Retail and ecommerce brands, plus food and beverage, entertainment and media, travel and hospitality, and fitness and wellness | Shopify ecommerce brands, from getting started to scaling SMS as a main revenue channel | B2C brands of all sizes, with retail, restaurant, wellness and enterprise pages | Ecommerce brands on Shopify and Shopify Plus, and other ecommerce platforms |
| Channels in the same platform | SMS, email, RCS and push | SMS, RCS and email | Email, SMS, reviews, helpdesk and the Klaviyo Data Platform | Email, SMS and web push |
| Pricing shape | Based on messages sent, list size, channels used and premium AI tools; free to install with a minimum 30-day trial, then month-to-month or long-term agreements | Published monthly SMS tiers from a Starter with a monthly minimum spend up to Enterprise on quote, plus per-message rates and carrier fees | Free plan, then listed monthly email and SMS plans that scale with contacts and credits | Free plan, then Standard and Pro monthly tiers by list size, with SMS added per message |
| Service model | 24/5 service with a dedicated support team, compliance tools on all plans | Postscript Plus managed service; Enterprise adds a dedicated Customer Success Manager | Free plan includes email support; AI agents for campaigns and support | 24/7 support including on the free plan, free 5-day migration from another email platform |
| Reason brands leave | Cost, and a roadmap that widened past SMS | Programs that send only occasional campaigns do not justify a separate SMS tool | Pricing increases, deliverability trouble, and billing tied to list size | Teams consolidating email and SMS into a larger platform |
| Typical switch | To Postscript or to Klaviyo SMS | From Attentive, or from a vendor with higher per-message rates | To or from Attentive, in both directions | Into a larger platform as the program grows |
Attentive
Attentive sells SMS, email, RCS and push from one platform, along with Attentive AI for campaign creation and Attentive Signal, an identity tag for recognizing more site visitors. TCPA and compliance tools are included with all plans, and service is 24/5 with a dedicated support team.
Pricing depends on messages sent, subscriber list size, how many channels you turn on and whether you want the premium AI tools. The App Store listing is free to install with a minimum 30-day free trial, after which you can take a month-to-month or a long-term agreement.
Two things push brands off it. The first is cost. The second is scope: teams that bought Attentive to run SMS hard do not always want the wider multi-channel roadmap, and reporting that compares journey and message performance is another reason brands look elsewhere. Brands running Attentive include 12th Tribe and 32 Degrees.
Postscript
Postscript is built for Shopify and leads with SMS, with RCS and email in the same platform. Plans are published: a Starter tier with a monthly minimum spend, then Growth, Professional and Enterprise on quote, each with per-message rates and carrier fees on top. There is also an AI Plan at a fixed monthly price that bundles Brand Center, Infinity Testing and Shopper, plus per-message rates. Billing happens after sending, with no prepaid balances or profile fees.
Per-message rates are a reason brands move here from another SMS vendor, and they are the reason to model your real send volume before you choose. The listed rates cover the US and Canada only.
Postscript Plus is the managed option, where in-house strategists create, run and optimize the program. It fits worst at the other end: a brand sending a campaign now and then has a hard time justifying a dedicated SMS tool against SMS inside its email platform. 1 Up Nutrition runs Postscript SMS Marketing on its storefront.
Klaviyo
Klaviyo positions itself as a B2C CRM: email, SMS, customer data, analytics, reviews and a helpdesk on one platform, with Composer for building campaigns and Customer Agent for support questions. Its Shopify app has a 4.7 rating across 3,433 reviews and launched in 2012.
Pricing is listed. There is a free plan with up to 250 profiles and 500 emails a month. On the App Store, the Email plan starts at a monthly price for 251 to 500 contacts and the SMS plan starts at a monthly price for up to 1,250 credits with carrier fees included. It also offers EU and US data residency and is SOC 2 Type II certified.
The pull is consolidation: one profile, one segment, flows that mix channels. The friction is the other side of that. Price increases as lists grow, billing tied to list size, and deliverability problems are reasons a brand starts shopping. Klaviyo also restricts some product categories, so confirm yours is allowed before you plan a migration. 100% PURE and 2XU run Klaviyo.
Omnisend
Omnisend covers email, SMS and web push with automation, segmentation and signup forms. Its Shopify app has a 4.7 rating across 3,200 reviews and launched in 2014. The free plan covers 250 contacts and 500 emails a month. Standard starts at 500 contacts and Pro at 2,500 contacts, both monthly and rising with list size. SMS is added per message on paid plans. Unsubscribed contacts are not billed.
Support is 24/7 on every plan including free, and there is a free 5-day migration from another email platform. It integrates with Shopify, Shopify Plus, Shopify Flow and Okendo among others, and can be driven from ChatGPT or Claude through MCP.
It fits brands running email as the primary channel with SMS as a supporting one. Brands leave when they want email and SMS in a single larger platform.
How to decide
On switching cost: the move itself is mostly list migration, consent records, flow rebuilds and a new number or re-verification. Omnisend offers a free 5-day migration from another email platform. The harder part is the contract you are already in, so time your evaluation before renewal, not after.
Questions people ask
Is it cheaper to run SMS inside Klaviyo or to use a dedicated SMS platform?
It depends on volume. Klaviyo lists a monthly SMS plan covering up to 1,250 credits with carrier fees included, which suits lower send volumes alongside email. Postscript publishes monthly tiers from a Starter with a minimum spend up to Enterprise on quote, with per-message rates and carrier fees separate, which is what you model when SMS volume is high. Attentive prices on messages sent, list size and channels used, so you have to ask.
Does bundling email and SMS with one vendor actually save money?
Attentive prices in part on how many channels you use, so the number of channels changes the quote. The tradeoff is concentration: one renewal, one deliverability reputation, one migration if it goes wrong. Price the bundle, then price the same volumes split across two vendors, and compare renewal terms rather than first-term terms.
How hard is it to switch SMS platforms?
Plan for list and consent record migration, number provisioning or re-verification, rebuilding flows and popups, and a period of watching deliverability. Omnisend offers a free 5-day migration from another email platform, and Attentive's App Store listing includes a minimum 30-day free trial so you can test before committing. The bigger constraint is usually your current contract term.