I own a Fritz!box for more than 3 years, so it's one of the older models. Even for the older models they still provide firmware updates which add new features.
It's very hack friendly: you just have to dial a specific number to enable telnet access, with a special web page you could get a packet dump (in wireshark/ethereal format) for any interface etc.
You can have multiple VOIP accounts and automatically select PSTN or a specific VOIP account based on the phone numbers prefix (or even block numbers this way). I've set this up so that emergeny and other free numbers gets send over PSTN, normal calls over one VOIP provider and calls to mobile phone over another VOIP provider. I've two phones connected and I've set them up, so that they ring all on incoming calls, no matter if the call comes from PSTN or one of the VOIP accounts.
And all from just one small box which never failed me. And even if it would fail - at least in Germany they provide a warranty of 5 years.