This function updates a customer account.

Note that for the purposes of the Cloud Fax and Notifications API, there are two kinds of customer accounts - "regular" or "XDDS" accounts, and "Fax2Mail" accounts. A "regular" account may have access to the usual messaging services of faxREACH, messageREACH and voiceREACH. A "Fax2Mail" account may have access to the fax-to-mail and mail-to-fax services.