Give your vendors access code with every invoice. Request your IT department to have all accounts payable agings dumped daily onto your website for access by your vendors. Print the website address and their unique access code on the bottom of their invoices so they may see their specific accounts receivable account, your accounts payable account, on your system. These balances will change every day with incoming new invoices or weekly payments, but it will help cut calls and make your vendors satisfied. Post their new status each day after hours so the information is current.
Security concern? If you are worried about allowing outside companies to view your internal server or data system, dump the account data each day on a separate server, disconnected from your internal company data. Dedicate that equipment or piece of hardware for outside internet access only.
Get them off your telephone – offer a current payment list. You might consider also dumping a list of all chronological payments made to the vendor. Include the check date (or ACH wire transfer date), check number if applicable and all invoices and credit memos paid, onto this same website. Allow vendors the ability to look online first before they are forced to call and wait on you to answer or return their call.