That's right. There is none. I think Citrix has a client, but you need their server, too.
Then there's VNC & SSH that you can search for.
In any case, Microsoft isn't likely develop or license anyone else to develop a Microsoft Terminal Services client for Symbian. If you absolutely must have that, and Citrix or VNC/SSH solutions are applicable, I'm afraid you need to get a PocketPC based phone instead.
If anyone ist looking to get Terminal Services on other devices then Microsoft. You should take a look at the Advanced Terminal Services Client. It is a Web Based Terminal Client so any Browser with enough support will be able to pull up this one. Maybe that helps I have not tried it yet on my P900 just got it. If not with the standard Browser then atleast mybe with the Opera Browser.
Microsoft's "web" terminal services client is an ActiveX control that works only with Internet Explorer on Windows. It loads and runs locally on the PC that accesses it with IE. It will, as the control is a Windows binary/executable, not run on Symbian OS.