Weeks one and two: run both, change nothing else
The risk in this move is not technical, it is that regular customers message a personal number out of habit and get no reply. So the first fortnight runs both. Staff keep answering where customers write, but every conversation is also recorded against the account, and outgoing messages start going out from the company number. Customers migrate because the replies come from there, not because they were told to.
Weeks three to six: the record becomes the source of truth
Once the traffic has shifted, the order draft replaces the mental note. Item, price, address and payment status are entered from the conversation, so the dispatch list at the end of the day is a list rather than a reconstruction across three phones. This is the point where the change starts paying, because a staff member being offline stops being a reason a sale waits until tomorrow.
Weeks seven to twelve: the numbers nobody had before
By the third month there is enough history to answer questions that were previously guesses: which products generate the most enquiries that never convert, which states have the worst delivery outcomes, how many transfers were claimed and never confirmed, and how many customers bought a second time. Those answers usually change what gets stocked and which logistics partners keep the business, which is a larger return than the tidiness of the inbox.