HP 4730 wont send/receive Fx

[Lasersupplies]

Hi, i have installed 1 x HP Laserjet 4730 in a customers office. They required faxing to be done from the copier. I have set everything fine, Phone Number, Region and Name. When i try to send the fax it dials out but does not seem to make a connection and this also happens when receiving. Does anyone know why this happening? The company are connecting the bt modem end to a cat5 converter and it is connect to a network point. The previous fax(an old of fax) works fine with it when its plugged in.
I have used a few different fax boards/formatters to no avail. I have lowered the baut rate but i am still getting nowhere. Has anyone come across this?

Many thanks

[Iowatech]

I was hoping someone would answer with the exact fix for this before me, as I've never seen this on HPs.
But I have seen something similar on other makes, and in those cases it was caused by some non-standard VOIP implementations (analog fax signal conversion to digital network traffic) being incompatible with the enhanced communication standards and features that are unique to newer fax enabled MFPs.
I don't know if this is possible on HPs, but turning off error correction in fax communications helped us somewhat. Other than that, you might need someone more versed in the network side of things to see it that place's setup is up to standard.
Hope that helps.