The Agent Communications Stack: Voice, SMS, and Email Unified
Most teams start by choosing channels one at a time. The result is usually three APIs, three billing systems, and three different operational habits. A unified stack matters because the agent does not think in channel silos.
What makes a communications stack feel unified
- Channel selection is deterministic rather than improvised
- Playbooks carry goal and persona across operations
- Human oversight exists where it needs to exist
- Operations, billing, and audit trails live in one system
Playbooks are the abstraction that makes the channels cohere
A playbook is not just prompt text. It is the durable statement of what the agent is trying to accomplish and how it should do it for a specific channel.
Calls and SMS are explicitly playbook-driven in the current CLI. Email uses inbox identities and drafts rather than the same playbook binding model, but it still sits inside the same workspace and operational flow.
spix --json playbook create --type call --name "Support escalation" --goal "Resolve the urgent issue or collect the right handoff details" --persona "Clear, calm, direct"
spix --json playbook create --type sms --name "Appointment reminder" --use-case delivery_notifications
spix --json phone bind +14155550101 --channel sms --playbook plb_sms_xyz789
spix --json phone bind +14155550199 --channel call --playbook plb_call_abc123 --inbound-default
spix --json email inbox create --username support --name "Support Desk"The channels do different jobs
Voice is synchronous and high-bandwidth. SMS is immediate and conversational. Email is formal, durable, and review-friendly. A unified stack matters because the system can choose the right one without changing operational context.
spix --json call create +15551234567 --playbook plb_call_abc123 --sender +14155550199
spix --json sms send +15551234567 --sender +14155550101 --playbook plb_sms_xyz789 --body "Reminder: your appointment is tomorrow at 2pm."
spix --json email send --sender [email protected] --to [email protected] --subject "Your case summary" --body "Here is what we resolved today."Operators still need oversight
Agents should not be left alone with outbound communication at scale. Draft review, transcript inspection, quarantined inbound handling, and durable records are part of the stack, not optional admin features.
spix --json email draft create --to [email protected] --subject "Feedback request" --body "We would love to hear how the rollout went."
spix --json sms accept msg_abc123