From the MTS site:
The 160 GB hard drive allows you to record up to 120 hours of Digital TV or 25 hours of High-Definition programming.
Since MTS uses MPEG4, they can store more hours of TV in the same amount of space compared to MPEG2 used by cable and sat. companies.
AT&T in the U.S. uses the same hardware and software and have been offering the Whole Home PVR for quite a while. This is what they offer:
Moto VIP1216 160GB, 133 Hours SD, 37 Hours HD
Moto VIP1225 250GB, 233 Hours SD, 65 Hours HD
Cisco IPN4320 320GB, 311 Hours SD, 87 Hours HD
The actual number of hours that can be stored in 160 GB will vary based on the content, so I'm not sure if MTS or AT&T is more accurate. The larger hard drives at AT&T are in very limited supply, so as they become more available hopefully MTS will start phasing them in.