Here’s how to differentiate which network someone in Kenya uses based on their phone number.  Numbers beginning with…

020 = landline operated by Orange

070, 071, 072 = Safaricom 

073 = Zain (now Airtel)

075 = yu 

077 = Orange 

In-network calls are cheaper than out-of-network calls, so most people use these to determine which SIM card to use when calling someone.  Could be a useful m-money authentication method?  For instance, an M-Pesa receipt that lists the sender as 075xxxxxxx would be fraudulent because 075 is a yu number.