Bulk SMS & Voice Broadcast Guide

Bulk SMS sends the same or personalized text messages to many recipients via registered sender IDs (headers) and templates. Voice broadcast (often called OBD — Outbound Dialer) plays a pre-recorded voice message to many numbers via 140-series, with options to collect keypress responses. Both are used for transactional alerts and campaign messaging, but they are different channels with separate DLT/template flows.

| Channel | Content | Sender ID | Template | Ideal For | Delivery States | | Bulk SMS | Text (160 chars, Unicode for regional) | Header (e.g., AX-AGILIS) | Content template | OTP, alerts, promotions | Sent → Delivered → Failed (DND, invalid) | | Voice Broadcast | Audio (pre-recorded) | 140-series number | Voice template/script where required | Reminders, surveys, OTP fallback | Answered → Unanswered → Busy → Failed | | WhatsApp Business | Text + media + buttons | WhatsApp Business number | WhatsApp template (separate from DLT) | Notifications, conversational | Sent → Delivered → Read (separate platform) |

Bulk SMS via DLT-registered headers and content templates (fixed + variable parts). Example template: 'Dear {name}, your OTP is {code} valid 5 min. - Agilis' where {name}/{code} are variables. Headers are sender IDs (e.g., AX-AGILIS) assigned to PE, templates pre-approved. Unicode supports regional languages (Hindi, Tamil etc.). Long SMS concatenated.

Voice broadcast uses 140-series numbers (TRAI-registered for promotional/commercial voice) and plays pre-recorded audio. States: Answered (human), Unanswered, Busy, Failed, plus IVR interaction (press 1). Unlike SMS, voice does not use DLT template in same way, but 140-series registration and consent still apply.

WhatsApp Business uses WhatsApp-approved templates (distinct from DLT), with media, buttons and read receipts. Do not merge WhatsApp rules with DLT/SMS rules — they are separate platforms with separate approvals, opt-in and 24-hour window. Use WhatsApp where customers prefer it and template categories align.

Per TCCCPR, Transactional is 30-min post-transaction (e.g., OTP within 30 min of transaction), Service is non-promotional informational (e.g., delivery update) with inferred/explicit consent, Promotional requires explicit consent and opt-out. Mixing promotional into transactional template is prohibited.

For bulk SMS, DLT requires PE registration, header assignment, content template registration (fixed/variable), and PE/header/Content ID transmission. Headers are 3–8 chars, templates have fixed and variable parts, one template should not be linked to multiple headers (TRAI). SMS via DLT; Voice via 140-series; WhatsApp via WhatsApp Business templates.

Scrub against NDNC/DND, handle Digital Consent Acquisition (DCA) via OTP where required, and honor preference (Fully Blocked, Partial). Inferred consent for existing customers vs explicit for prospective. Promotional must offer opt-out in same message (TCCCPR 2025).

Segment by language, city, purchase history, or campaign. Personalize with fields: dear {name}, order {order_id} . Test personalization with real data to avoid broken variables.

Unicode supports Hindi, Tamil, Telugu etc., but counts as 70 chars per segment vs 160 for GSM-7. Long messages concatenated. Test rendering on multiple handsets.

SMS states: Sent → Delivered → Failed (DND, invalid number, template mismatch, DLT chain mismatch). Voice states: Answered, Unanswered, Busy, Failed. Retry logic: schedule retries for Failed/Unanswered with backoff; do not retry DND failures.

Schedule for optimal delivery windows (e.g., 10 AM–6 PM for promotional per TRAI, transactional 24×7 where allowed). Recurring broadcasts for reminders, renewals. Plan segments, headers, templates, and consent before scheduling.

| Use Case | Best Channel | | OTP / Transactional alert | Bulk SMS (fast, low cost) | | Promotional to opted-in | Bulk SMS (if DLT template) or Voice (if voice template) | | Survey with keypress | Voice Broadcast (IVR input) | | Payment reminder (high open) | Voice (answered) + SMS fallback | | Conversational follow-up | WhatsApp (if template approved, not SMS DLT) |

- Are PE, headers, templates registered and linked, with chain defined? - Are you using correct header-template pairing, not promotional under Service? - Are URLs/APKs whitelisted where required? - Are consent/DND scrubbed and opt-out in promotional? - Have you tested with small segment and provider delivery reports? - Are you distinguishing SMS DLT vs Voice 140 vs WhatsApp Business rules?