The test call forwarded to my mobile appeared as € 0,00 so I believe there is no problem in that area.
I've had Orange FTTH for ~16 months now, with little trouble. Once, I called support because the TV had stopped working and rebooting everything did not help. They reset something at their end and had me reboot again; it's been fine since. AFAIK, there has been only one Internet outage. It occurred at ~3 AM and lasted a couple of hours; possibly it was just scheduled maintenance, though no notice was given. Otherwise, the only other problem was some billing errors in my favor. Orange discovered them a couple of months later and made a retroactive charge. But yes, their CGV will give anyone a headache.
Thanks for telling me about OVH -- their personal SIP line looks like a good value for various applications. How is the quality and reliability?
Sorry, I may have given you mis-information about CallWithUs. You may not be able to set up forwarding directly on their site, i.e. you would need to bridge through your OBi or a PBX service; ask their support whether it's possible.
I've never used Sonetel, though there was a recent thread about them, mostly positive.
http://www.dslreports.com/forum/remark,27172249 . Among others, Anveo and
VoIP.ms also include some PBX features with their services.
Many companies offer measured DIDs and/or DIDs that include some usage and are billed per-minute after that. For example Anveo has "value" DIDs with 40 minutes free per day (more on paid accounts) and unlimited DIDs at a higher monthly cost. With CallWithUs, it's more complicated, because they buy from several vendors. You may find one number with 3000 free minutes/month included, and another in the same area that is pay-per-minute only.