Many mystery shopping companies offer some phone shops, but usually not many for any given company. Fees range from $1 for some Corporate Research is currently doing through more elaborate scenarios and reports. I have done some that have paid as much as $25, but they are rare. The average phone shop is in the $3-5 range and takes usually 20-30 minutes to do and report.
Places that have them are Market Force through the Blue Portal of their shops, Informa, Cross Financial and others. Use the "Search" feature at the top of the main page of the forum and look for "phone shops" in the past 6 months as this topic comes up from time to time and shoppers chime in with ones they have seen or done.