An 0800 number means the business pays for the call instead of the caller. That is the entire mechanic. Everything else is about whether it changes behaviour enough to be worth the cost.
Who pays for what
An ordinary number, mobile or landline, is paid for by the person calling, at their network’s normal rate. It costs you nothing to receive.
A toll-free number is free to the caller and billed to you, per minute, for every call.
That inversion is the decision. You are buying the removal of a small barrier, and paying for every call that comes through it — including the wrong numbers, the sales calls, and the person who rings to complain about something unrelated.
When it is genuinely worth it
When the caller has no relationship with you yet. A first enquiry from someone comparing suppliers. Removing any friction matters more when they have three other numbers to try.
When your customers are price-sensitive about airtime. This is real in parts of the Kenyan market and worth taking seriously rather than dismissing.
When you are asking people to report something. Faults, complaints, safety issues, anything where you want to hear about a problem you would otherwise not hear about. Charging people to tell you bad news is a poor trade.
When it is a credibility signal. An 0800 number reads as established. For some buyers that matters.
When it is not
For existing customers with an account. They will ring you anyway. You are paying for calls you would have received free.
For a support desk with long calls. You are now paying by the minute for every technical support call. Model that against your actual handling time before committing.
When you have not fixed the queue yet. Paying for calls you then fail to answer is the worst of both worlds.
As your only number. See below.
The arrangement that usually works
Have both.
An ordinary Kenyan number — mobile-format is the most answered — as your main line, printed everywhere, used by existing customers. And a toll-free number used specifically where removing the barrier pays: on the advertisement, on the pack, on the complaint channel.
Both can ring the same team. The system knows which number was dialled, so you can route them differently and, more usefully, report on them separately. After a month you will know what each one actually brings in, which turns the question from an argument into arithmetic.
What to ask before buying one
What is the per-minute cost to me, inbound? The whole economics sits here.
Can it be reached from all networks? Including the one your customers mostly use. Test it, on a real handset, before you print anything.
Does it work from a landline? Not always, and not always obviously.
Is it portable? If you leave the provider, does the number come with you? This matters enormously once it is printed on a building.
What happens out of hours? You are paying for the call either way, so make sure something useful happens.
The number format question
The broader decision — landline, mobile or toll-free — has more to it than cost. A mobile-format number is answered more often when you call out. A landline format reads as settled. A toll-free number reads as corporate.
There is a fuller article on choosing a number format, and one on moving the number you already advertise.
Our own position
One Kenyan number is included with every plan, and additional numbers are KSh 1,000 a month each. Toll-free numbers are available on request and priced separately, because the inbound minutes are a real cost that varies with how much you use it.
We would normally suggest starting with an ordinary number, getting the queue and the menu right, and adding toll-free once you know what you are paying per useful conversation.