Typical image rejection

Hi,

Can someone tell me a typical image rejection requirement (regarding the Zero-Order-Hold images of the ADC) for a typical RF transmitter (say, GSM/LTE/UMTS)?

I build system-level simulation and I design the reconstruction filter for the ZOH-DAC and the one reason for my question is that I just want to start off with something that's not entirely unrealistical.

Will you typically use a Butterworth filter for that or something else? If Butterworth, what are the typical filter orders employed? 3rd order or more like 7/9th order?

Thanks