As far as I know under certain Ec/No the connection goes into compress mode in order to optain measurements from different frequencies for inter-frequency or inter-RAT handover. And after the decision process in RNC it is decided to perform the measurements.
By blind/rescue etc. I meen that you can perform a handover without entering compressed mode thus without measurement reports from the GSM network. Which is very usefull if you have colocated GSM/DCS sites with UMTS sites. Do you mean that this one is possible in Ericsson let’s say in P4?