Four options, and they differ far more in what they recover than in what they cost.
Option 1: voicemail
Cost: nothing. Recovers: very little from strangers.
The reason is simple. Someone comparing three suppliers at 9pm will not leave a message for one of them and wait. Voicemail works for customers who already know you and are prepared to wait; it does almost nothing for acquisition.
Option 2: an on-call rota
Cost: the highest, in money or goodwill. Recovers: the most for genuine emergencies.
If your work includes real emergencies — burst pipes, no heating in January, locked out — someone answering is worth what it costs. For everything else it is a very expensive way to answer "what are your prices".
Option 3: a phone answering service
Cost: per call or per minute, so it rises with volume. Recovers: phone enquiries, as messages.
Genuinely useful if your phone rings out of hours. Two limits: it only covers the phone, and what you get is a message rather than an answered question. The customer's problem is still unresolved.
Option 4: AI on the website
Cost: flat monthly, typically the lowest per enquiry. Recovers: website enquiries, answered rather than acknowledged.
Covers the channel where most out-of-hours browsing actually happens, answers the question rather than taking a name, and does not charge more in a busy week. It cannot answer your phone.
The comparison that actually decides it
Not cost. Channel.
Open your analytics, segment by hour, and look at what happens between 6pm and 8am and at weekends. Then compare it to your out-of-hours call log.
If the website number is bigger — for most businesses now it is — then an answering service is covering the smaller half of the problem at the higher price.
The combination most businesses land on
AI on the website for everything, an on-call number surfaced only for genuine emergencies, and voicemail retired.
That covers the volume cheaply and the urgent properly, which is the right shape.
Check yours
Build an AI employee from your website and ask it what a 10pm visitor would ask. It takes about a minute and costs nothing.
Related: what missed enquiries cost · AI receptionist vs answering service.