sipgate basic is a prepaid, Pay As You Go phone service without set up charges, recurring service fees or minimum spend requirements.
Calls to other sipgate phone numbers, UK freephone 0800 number and to UK 999 Emergency Services are free of charge. (Never, ever test call 999.)
All you need to do to keep your sipgate basic service active is to login online and make or receive a VoIP call at least once every three months. There is no requirement to add call credit to keep your sipgate basic account and phone number active.
You'll need to add credit to your account to use some functionality, like placing phone calls to other networks or to send web SMS.