Just so that future visitors discover the right answer to this question: the above commenter is not correct. You can fix this problem by changing several options in the web.config. Here is how mine is set up:
<system.serviceModel>
<services>
<service name="ourWebService.ourService" behaviorConfiguration="ourWebService.ourServiceBehavior">
<host>
<baseAddresses>
<add baseAddress="http://oursitename.com:83/ourService.svc" />
</baseAddresses>
</host>
<endpoint bindingNamespace="http://oursitename.com:83/ourService.svc"
address="" binding="basicHttpBinding" contract="ourIWebService.IourService"
bindingConfiguration="customBinding2">
<identity>
<dns value="oursitename.com" />
</identity>
</endpoint>
<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
</service>
</services>
<bindings>
<basicHttpBinding>
<binding name="customBinding2" >
<readerQuotas maxArrayLength="2147483" maxStringContentLength="2147483647" maxNameTableCharCount="2147483647" />
</binding>
</basicHttpBinding>
</bindings>
<behaviors>
<serviceBehaviors>
<behavior name="ourWebService.ourServiceBehavior" httpGetUrl="http://oursitename.com:83/ourService.svc">
<serviceMetadata httpGetEnabled="true" httpGetUrl="http://oursitename.com:83/ourService.svc/mex"/>
<serviceDebug includeExceptionDetailInFaults="true" />
</behavior>
</serviceBehaviors>
</behaviors>
</system.serviceModel>
The important bits are the get urls, the identity, and the baseAddresses.