Hello
I am doing it!! You only need 4p in RJ11 and a USB/TTL module, CP2102 or PL2303hx (I read that the CP2102 was better, I have CP2101 and waiting PL2303HX...). I think you neet to use a voltage divide too like Bluetooth module. More important is driver for your windows ;-)
http://www.silabs.com/products/mcu/pages/usbtouartbridgevcpdrivers.aspx
And for PL2303hx looking for "PL2303_Prolific_DriverInstaller_v1.8.19", I read that with v1.9 DON´T WORK
I made the cable with CP2102 direct to RJ11 and don´t work!!!
In this page, send the cable and says work at 3,3V
http://teleskopy.pl/product_info.php?currency=EUR&products_id=3376&language=en&lunety=Przewód_kabel_USB_do_SkyWatcher_Virtuoso,_d³ugo¶æ_2_metry
P.D. If you are going to put a couple or resistor,I think that 4,7K and 10K is better.... My GoTo mount, with the mount BT, was broken. I used 47 ohm and 100 ohm and work a few minutes, but then...
When I get the whole summary working