TL;DR — When to Pick Which
Use SMS for OTPs, banking alerts, and any time-critical message where guaranteed delivery to every Indian phone (smartphone or feature phone) matters more than rich content. SMS is regulated by TRAI's DLT framework, costs ₹0.12-0.18 per send, and delivers in seconds.
Use WhatsApp Business API for conversational engagement, rich media (images, documents, buttons), abandoned cart recovery, and customer support — where the user is on a smartphone and the message benefits from rich formatting. WhatsApp is regulated by Meta, costs ₹0.18-1.00 per conversation depending on category, and supports 24-hour conversation windows.
The honest answer for most businesses: use both, route by use case. The Spring Edge SMS API and WhatsApp Business API run from the same account, share one wallet, and route via one set of webhooks — so multi-channel doesn't mean multi-vendor.
Full Side-by-Side Comparison
WhatsApp Business API vs SMS across the dimensions that matter for Indian businesses in 2026.
| Criteria | SMS | WhatsApp Business API |
|---|---|---|
| Reach | ~99% of Indian mobile numbers (smartphone & feature phone) | ~500M+ users in India (smartphone only, with WhatsApp installed) |
| Regulator | TRAI / DLT framework | Meta + TRAI (separate processes) |
| Cost (transactional / authentication) | ₹0.12 — ₹0.18 per SMS | ₹0.18 — ₹0.30 per conversation (24h) |
| Cost (utility / order alerts) | ₹0.12 — ₹0.18 per SMS | ₹0.30 — ₹0.50 per conversation (24h) |
| Cost (marketing) | ₹0.10 — ₹0.16 per SMS (promotional) | ₹0.78 — ₹1.00 per conversation (marketing) |
| Delivery time | < 3 seconds (direct routes) | < 5 seconds typical |
| Open rate | 98%+ (transactional), 30-40% (promotional) | 95%+ within first hour |
| Rich media | Text only (160 chars / 70 Unicode) | Images, documents, video, audio, location, buttons, lists |
| Two-way conversation | Limited (requires virtual long-code or short-code) | Native — replies free within 24h service window |
| Template approval | DLT (24-48h, per operator) | Meta (minutes for Auth/Utility, up to 24h for Marketing) |
| DND restriction | Promotional blocked for DND; transactional unrestricted | No DND concept; user can block your number |
| Time-of-day restriction | Promotional 9 AM-9 PM only; transactional 24/7 | None (Meta-side); IST common-sense applies |
| Session window | N/A (single send) | 24-hour conversation window after user message |
| Reach feature phones | Yes | No |
| Best for | OTPs, banking alerts, mass-reach broadcasts, feature-phone audiences | Conversational engagement, rich-media transactional, support, abandoned-cart recovery |
Cost Deep Dive: Per-Message vs Per-Conversation
The single biggest mental model shift between SMS and WhatsApp Business API is the billing unit.
SMS = Per Message
Every SMS sent is one billable unit (1 credit = 1 SMS for English content up to 160 chars). Send 100 SMS, pay for 100 SMS. Simple. Long messages auto-split into multiple credits (306 chars = 2 credits, etc.). Unicode (Hindi, Tamil) is 70 chars per credit.
WhatsApp = Per Conversation (24-hour Window)
One "conversation" lasts 24 hours and includes all messages exchanged with one user during that window. Send 5 messages to the same user in 23 hours = 1 conversation = 1 billable unit. Send 5 messages to 5 different users = 5 conversations.
Conversations come in four pricing tiers based on the first message in the window:
- Authentication (OTPs, login codes) — ₹0.18-0.30 per conversation
- Utility (order, payment, delivery alerts) — ₹0.30-0.50 per conversation
- Marketing (promos, sale, re-engagement) — ₹0.78-1.00 per conversation
- Service (customer-initiated reply, free within 24h) — free
Worked Example: 1 Lakh Order Confirmations + 3 Updates Each Per Day
Hypothetical e-commerce: 1,00,000 orders / day, each customer gets order confirmation + dispatch + out-for-delivery + delivered (4 messages within 48 hours).
- SMS: 1,00,000 customers × 4 SMS = 4,00,000 SMS × ₹0.13 = ₹52,000/day
- WhatsApp: 1,00,000 customers × 2 conversations (one per 24h window) × ₹0.40 (Utility) = ₹80,000/day
SMS is ~35% cheaper here because the per-message economics favour multiple short sends. But: WhatsApp messages can include the dispatch tracking link inline, the delivery photo, and a "rate this delivery" button — engagement value that may justify the premium for D2C brands.
Worked Example: Marketing Campaign to 10,000 Users
- Promotional SMS: 10,000 × ₹0.13 = ₹1,300
- WhatsApp Marketing: 10,000 × ₹0.85 = ₹8,500
SMS is ~6.5× cheaper for one-off marketing blasts. WhatsApp wins only if the rich content drives meaningfully higher conversion (which it often does for D2C, but not always for B2B).
Pick by Use Case
Use SMS for…
- OTPs and authentication — cheapest channel that reaches every Indian phone
- Banking alerts — RBI compliance preference, plus DND-exempt delivery
- Feature-phone audiences (rural, Tier 3) — WhatsApp doesn't reach
- Mass promotional broadcasts at scale (> 100K users) — cost dominates
- Time-critical short alerts (fraud, security) — lowest latency
- Recipient consent unclear — SMS works without prior WhatsApp opt-in
- Government / PSU communication — SMS is the official record-of-delivery channel
Use WhatsApp Business API for…
- Order confirmations with rich detail — product image, total, tracking link, button
- Customer support replies — free within 24h service window
- Abandoned cart recovery — conversion 3-5× better than SMS or email
- Onboarding flows — multi-step interactive guidance with buttons
- D2C / e-commerce engagement — user is already on smartphone with WhatsApp open
- Conversational AI / chatbots — native two-way without virtual numbers
- Premium fintech UX — rich account statements, document delivery
The Hybrid Approach Most Businesses End Up With
Most businesses at scale don't pick SMS or WhatsApp — they use both, routed by use case and recipient profile. Common pattern:
- OTPs: SMS first (every Indian phone), WhatsApp as fallback if user opts in. Sub-3-second delivery, lowest cost.
- Order confirmation: WhatsApp if user has WhatsApp installed (enriched UX), SMS fallback for the rest. Most modern Indian e-commerce platforms route this way.
- Marketing campaigns: SMS for broad mass-reach (cost), WhatsApp for high-value/high-converting segments (engagement).
- Customer support: WhatsApp inbound, SMS outbound for follow-ups outside the 24h service window.
- Voice OTP fallback: for DND users or when SMS fails repeatedly — covered by Voice OTP.
Spring Edge runs SMS, WhatsApp Business API, and Voice from a single API surface, with one wallet and one set of delivery webhooks — so multi-channel doesn't mean multi-integration. See the API documentation.
Regulation: DLT (SMS) vs Meta (WhatsApp)
SMS — TRAI's DLT Framework
Every commercial SMS to an Indian number requires a registered DLT entity, an approved sender ID, and a pre-scrubbed template. Approval takes 24-48 hours per template. The framework applies to all four operators (Jio, Airtel, Vi, BSNL). Once approved, templates are auditable and compliance is enforced at the operator level. DLT registration guide.
WhatsApp — Meta's Business Platform Policy
Every WhatsApp Business API account requires Meta business verification (1-3 days), a dedicated phone number, and per-template approval by Meta. Authentication and Utility templates approve in minutes; Marketing templates take a few hours to 24 hours. Quality rating affects daily send caps — new numbers start at 1,000 unique recipients/day, scaling to 100K+ based on quality.
The Combined Compliance Stack
For businesses using both: DLT for SMS + Meta for WhatsApp. Spring Edge handles both compliance flows from one onboarding — you submit business documents once and we propagate to DLT portals and Meta business verification in parallel.