  We present a comparison between the published optical, IR and CO
spectroscopic redshifts of 86 (sub-)mm galaxies and their photometric redshifts
as derived from long-wavelength radio-mm-FIR photometric data. The redshift
accuracy measured for 13 sub-mm galaxies with at least one robustly determined
colour in the radio-mm-FIR regime and additional constraining upper limits is z
\~0.3. This accuracy degrades to z~0.65 when only the 1.4GHz/850um spectral
index is used, as derived from the analysis of a subsample of 58 galaxies with
robustly determined redshifts. Despite the wide range of spectral energy
distributions in the local galaxies that are used in an un-biased manner as
templates, this analysis demonstrates that photometric redshifts can be
effciently derived for sub-mm galaxies with a precision of Delta z < 0.5 using
only the rest-frame FIR to radio wavelength data, suficient to guide the tuning
of broad-band heterodyne observations (e.g. 100m GBT, 50m LMT, ALMA) or aid
their determination in the case of a single line detection by these
experiments.
