What a shared inbox costs when conversations are metered

The short answer

Conversation metering links your monthly software invoice to how often customers decide to reach out. You do not control when buyers ask about stock, chase a shipment, or reply twice, so the software cost moves without you touching it. The largest bills arrive during heavy sales periods, product incidents, and marketing campaigns.

How the meter works

Most shared inbox meters descend from the billing structure of the WhatsApp Business API. Meta groups WhatsApp messages into time windows. An inbound message to a verified business number opens a 24-hour customer service window, and inside that window the business can send free-form replies without per-template fees. Outbound notifications sent outside the window need pre-approved templates and carry per-message fees set by the template category.

Software vendors put a second meter on top of Meta's network fees, and the window length is theirs to choose. Trengo, for example, defines a conversation as any reply to an inbound or outbound message with a customer inside a 7-day window, and a message outside that window starts a new one.

Timeline of a metered conversation window:

Hour 0                Hour 12               Hour 24               Hour 26
  |---------------------|---------------------|---------------------|
Customer says:        Agent answers:        Window closes.        Customer asks:
"Is this in stock?"   "Yes, blue or red?"                         "Blue please."
[ Conversation #1 starts ]                  [ Window ends ]       [ Conversation #2 starts ]

Each vendor writes its own contract definition for what starts a new billable event. Some run a 24-hour clock. Some run seven days. Some count any thread an agent marked resolved as finished, so a "thank you" two minutes later opens a new billable conversation. Find that definition in the vendor's own terms before you sign.

What counts as a new conversation

Common triggers across vendors:

• A customer replies to an old thread after the platform window closed.
• A buyer sends a second message chasing an open order.
• An automated satisfaction survey or bot follow-up reopens a closed thread.
• An outbound broadcast collects an automated out-of-office reply.
• A client writes from a second phone number or a different email address.
• A member of a group chat sends a message, and the vendor counts a conversation for that participant.

The last two vary most between vendors, and the group chat rule is the one that surprises operations teams.

Why the invoice grows when the business does well

A conversation meter charges more when commercial activity increases. Advertising spend produces inbound interest. A product launch fills the queue with questions. A winter storm that delays delivery vans produces hundreds of people asking where their order is.

Under conversation metering, each of those events raises the software bill in the same billing cycle where delivery costs, stock purchases, or ad spend are already at their highest.

The model also creates a bad incentive. Agents who know that open threads cost money start closing conversations early, the customer replies with a clarifying question, and that reply opens another billable conversation.

Three worked examples

These three examples use Trengo's published Boost pricing on annual billing, read from trengo.com/prices on 24 August 2026: EUR 299 a month, 10 users included, 6,000 conversations included across the year, EUR 15 per 100 conversations above the allowance, and EUR 25 a month per user above the ten. On monthly billing the same plan is EUR 349 a month with 500 conversations a month, extra conversations at EUR 18 per 100, and extra users at EUR 30.

That difference matters on its own. Annual billing pools 6,000 conversations for the whole year, so a busy spring eats the allowance that December needed. Monthly billing gives 500 a month and resets.

Scenario one: a small desk

Three people handling 400 customer conversations a month.

• Staff: 3
• Monthly volume: 400 conversations
• Annual volume: 4,800 conversations
• Base cost: EUR 3,588 for 12 months
• Overage: EUR 0
• Total: EUR 3,588

The desk never reaches its allowance. It still pays EUR 3,588 across the year, which is EUR 1,196 per person for a shared inbox.

Scenario two: a support team that grows

A support department reaches 12 staff while volume climbs through the year.

• Volume: 500 a month in Q1 (1,500), 800 in Q2 (2,400), 1,200 in Q3 (3,600), 1,600 in Q4 (4,800)
• Annual volume: 12,300 conversations
• Base cost: EUR 3,588 for 12 months
• Extra users: 2 above the 10 included, at EUR 25 a month: EUR 600
• Overage: the 6,000 allowance runs out during month eight, leaving 6,300 conversations at 63 blocks of 100 for EUR 945
• Total: EUR 5,133

In December the team handles 1,600 conversations. That invoice is EUR 299 base, EUR 50 for the two extra users, and EUR 240 for 16 blocks of overage, so EUR 589 against the EUR 299 paid in January. The work went up and so did the unit cost of doing it.

Scenario three: a seasonal spike

An online retailer with eight staff, steady for ten months, then a holiday peak.

• Ten baseline months: 700 conversations a month (7,000)
• November: 2,600 conversations
• December: 3,400 conversations
• Annual volume: 13,000 conversations
• Extra users: EUR 0, because eight staff fit inside the ten included
• Base cost: EUR 3,588 for 12 months
• Overage: 7,000 conversations above the allowance, at 70 blocks of 100 for EUR 1,050
• Total: EUR 4,638

The allowance runs out during month nine, so both peak months bill in full. December needs 34 overage blocks for EUR 510 on top of the EUR 299 base, which is an EUR 809 invoice in the month when cash is already committed to stock and advertising.

How to audit a vendor pricing page

Before signing an order form for a shared inbox, work through the commercial terms in this order:

1. Find the vendor's definition of "conversation". It might mean an open ticket, an inbound message, or a rolling window, and those three produce very different bills.
2. Find the window length. Some run 24 hours, some seven days, some hold open until an agent clicks resolve.
3. Check the reset period on the allowance. An annual allowance hides the cost step until month seven or eight.
4. Ask what happens on the day you cross the allowance. The software either blocks messages, throttles delivery, or bills the overage to your card.
5. Confirm whether inbound questions and outbound replies both count.
6. Ask whether internal comments and collaboration notes count as platform activity, and get the answer in writing.
7. Ask how group messages on Telegram or WhatsApp are counted. One message in a 20-person group can register as one conversation or as twenty.
8. Read the user table by permission level. An accountant or a warehouse manager who only reads threads may still need a paid seat.
9. Look for a second meter on the AI features. Get the contract definition of a resolution or an outcome, and ask whether a failed answer still bills.
10. Check retention and export rights on the tier you are buying rather than the top one, including which file formats you receive on termination. Our guide to conversation history retention covers what to look for.

Pull your own conversation logs for the past 12 months before you evaluate any proposal. Vendor estimates of your volume tend to be lower than your volume.

What a fixed meter looks like

CommunicationOS meters connected accounts instead of conversations, which is a number an operations team can count on day one and plan against.

Teammates are included on every tier. Message volume is not metered. The Team plan is USD 79 a month for 10 connected accounts with 10 GB indexed, as set out on the pricing page.

The retailer in scenario three pays USD 948 for the year on CommunicationOS, or USD 792 billed annually, against EUR 4,638 on a conversation-metered contract. The December invoice matches the January invoice however many thousands of shoppers write in. Uptime commitments and the service credits attached to them are set out in the service level agreement.