It depends on your contract. Most will take your payment then phone you. Please note that if you don't call first, you will get a "ding" on your credit report. The reason for this is that if they don't change your payment amount in the computer FIRST, then the when the credit reporting program is run at the end of the month, it will note you as "delinquent" and report that to the credit bureaus. You see, "delinquent" may be due to under-payment or non-payment.
Note that in addition to paying a fee, lenders are obligated under contract to provide information about payment progress to the credit bureaus in exchange for their capability to pull data about prospective borrowers.
Most lenders are willing to help get you by a "hump". They don't want you to "skip".
Hope this helps.