hi all,
Just thought I'd share this to help you save the same money as me on your CCNA-Voice lab.
The PVDM-12 will work quite happily in a 1760 router! I know all docs will say that it is meant for the NM-2HDV but I have got one working.
I bought a 1760 off ebay to run as a FXS/FXO gateway for my CCNA Voice studies. whilst looking for a PVDM-256-8/12, which were selling for around £100 -£200 (the router was only £20!!) I came across a PVDM-12 being listed as suitable for a 1760 - It was only £10 so I went for it. I thought to myself, "well, if it doesn't work I'll probably get the £10 back by re-listing it on ebay"
It came last week and I fitted it to my router - and to my surprise it gave me 3 DSP resources and my FXO card is now working perfectly connected to my landline

Obviously, i wouldn't recommend it in production, but I would have struggled to afford the pvdm-256 so was a treat for me
Not sure if IOS version would affect this, am running a 12.2 IPvoice image
So, as the 1760 supports 2 PVDMs this could give you 6 DSP resources for £20.
CCNA Voice exam tomorrow
Chris