To send 1 SMS unit (160 characters) to a UK mobile number will use 1 credit. It is possible to send longer messages, but this will mean spending multiple credits. We use a tiered pricing structure dependent on the volume of credits being purchased.
It is a pay-as-you-go service where you top up and buy credits when you need them. Once purchased, credits don’t expire - so you don’t need to worry about them disappearing.
Please note that if you send a message which contains a Unicode character it will reduce the character count from 160 characters to 70 characters per credit.