Hi,
For Voice, the sandbox is not operational .
The get a number for testing, the process is automated:
Log in to your Account>click on the app>Voice> Phone number>Under Voice-Phones>fill in the request form>(Product section)>Voice Service>Country> agree to terms>Category>select "Test Number" on the voice form.
You will be issued with a live number to use in the production account for a 2 weeks test period after which it will be removed. Please note to configure your callback, top up your account and proceed to make calls.
Kindly reach out to voice@africastalking.com for technical assistance.