Add up the digits in each of the customer numbers of the customers you talk to on the phone? Reduce to a 0-9 range and treat as a d10 roll
Or, since they're a number from 0-9 anyway, use them as a random string. However, that'd take a while. With the lack of calls lately, I'm only getting 20-30 calls a day, that's only 180-270 integers, adding up to 240 more if I use account numbers... That'd be doable. Save over 2-3 days...