CASE STUDY · 2026
DTMF to voice switch
Bilingual end to end
Voice agent fleet · One number, two languages
Result: DTMF dropped, spoken switch, confirmation mid-call
01 / THE PROBLEM
One phone number, callers in French and in English.
The demo gateway answers on a single number and routes to seven verticals by spoken keywords. Every caller had to be able to pick their language in the first seconds, without the agent getting it wrong.
02 / THE CONSTRAINT
I tried DTMF first, "press 0 for French".
Inbound DTMF did not fire reliably on the telephony integration. A pressed key could simply never reach the agent, and the caller stayed in the wrong language without knowing it.
03 / WHAT I CHOSE
I rebuilt it all as a spoken switch, with confirmation before changing language.
The caller says the language instead of dialling it. At the greeting, they say "français" and the agent switches at once. Later in the call, any change of language goes through a confirmation, so a misheard word never changes the language of the call by accident.
04 / WHAT IT DOES TODAY
How a call crosses the gateway, from the single number to the agent for the right vertical.
- 01
Incoming call
one phone number
- 02
Greeting
the agent introduces itself,
then: "pour continuer en
français, dites simplement
français"
- 03
Language
"français" at the greeting:
immediate switch
later: confirmation
first
FR / EN
- 04
Routing
spoken keywords,
to the right vertical
7 verticals
- 05
Vertical agent
qualifies, books,
sends the text,
transfers
05 / WHAT I WOULD CHANGE
Every call starts in English. For a French speaker I already know, that step should not be there at all.
The voice platform can call a webhook before the call is even answered, carrying the caller number. From there I can look up the language that number used last and open straight in it, without asking anything. I have not done it yet: my own fleet audit showed that webhook is unused across all 12 agents. The spoken switch would stay, as the net for numbers I do not know.
A problem like this at your place? Describe it.