validateKenyanNumber function
validateKenyanNumber checks if a number is either has either prefix of '+254111', '+254110', '+254100', '+2540101', '+254102' or '+2547xx'
Implementation
bool validateKenyanNumber(String phone) {
final String fifthChar = phone.substring(4, 5);
if (fifthChar == '7' || fifthChar == '1') {
return true;
} else {
return false;
}
}