1> Perform a drivetest and check that you can perform a call setup. A drivetest trace is the first step to understand this kind of problem. Also, at OMC-R, ensure, the cell is not locked, not barred, etc. Ensure that all parameters follow default recommendations from Alcatel
2> what do you mean “same position” ? GSM900 antennas and DCS1800 antennas can be colocated on the same mast, but you must ensure few centimeters between them. From memory, i would say something like less than 30cm.