My two cents:
AT&T Uverse is VDSL service: http://en.wikipedia.org/wiki/U-verse Think DSL, but much faster.
To summarize much research: AT&T provides a 2Wire modem/router (A.k.a. RG or Residential Gateway) that can connect to a neighborhood DSLAM (Large vented metal cabinets) via RJ11 (phone lines) or to a NID (Network Interface Device) attached to the building via RJ11, COAX, or Ethernet, whichever is easiest based on how the home is wired. COAX can alternatively (not both) be used inside the home for HomePNA networking to connect the various IPTV tuners to the 2Wire. In fact, if the tuner is connected using Coax, you can plug something in to the tuners empty ethernet jack and be on the network. (It acts as a bridge) You can also connect the IPTV tuners via ethernet and even WiFi. There may be issues related to multicasting depending on the additional equipment in the mix. (Applies to IPTV service)
I believe (haven't seen it yet) that the only difference between the commerical and residential versions is simply that AT&T doesn't offer the TV programming on the commercial accounts.
Having had Uverse installed last week and been playing with it:
1) the 2wire does not visibly support QoS
2) You can attach a router to the 2wire, and disable the warnings about doing so.
3) If AT&T will sell you additional static IPs, the 2wire can pass them through (bridge mode)
4) If you have TV or Telephone service through AT&T, they will take priority over Internet, defeating any QoS provided by a seperate router (as would connecting anything directly to the 2wire but the 2nd router, whether wired or wirelessly)
5) The 2wire phone jacks work as a standard SIP ATA, but are locked down unless you purchase phone service from AT&T. However, the SIP ALG (application layer gateway) is eanbled whether you purchase phone service from AT&T. This CAN cause problems with SIP phones and/or servers, but it can be disabled. It is likely, but I haven't tested this yet, that there are hidden QoS features to provide a boost to SIP. It seems probable because of the ALG support.
6) Uverse is known for having highish latency, that COULD be an issue with VOIP phone service. I strongly suspect it is simply due to sharing the internet/VDSL connection with TV service, and likely a non-issue if you dont have TV service.
Modems - which means alarm systems, some fancy DVR's (DIsh network, Tivo) and credit card processing machines, pretty much are NOT supported over VOIP/SIP. You might get lucky if you have pristine high quality connections but it is much preferable to switch to alternative methods. DVRs and Credit cards over the internet, and some other means of connecting entirely for the alarm system (internet, cellular, radio) If there really is no alternative for the alarm system, ask your telephone company about metered service for that single line. You pay for every minute of an outgoing call, but as it should be rarely used, you can likely get the bill down to $7-15 a month.
Faxing - Asking "Can you send it/Can I send it via email" works surprisingly well. Like, nearly always. Failing that, Vitelity.com offers faxing via email/web site for $3 a month plus $.03 a minute. You need to be able to attach a document, or if it needs to be marked up with a pen, scan in, and attach a document. Receiving faxes can be done via the web page or email, never using paper at all. Other companies provide similar services. Yes you can fax using an ATA, no, you really don't want to mess with it
If the internet goes down, nearly every SIP trunk provider will let you specific an alternate means to route a call for each DID you have. (Direct Inward Dial, your phone numbers in other words.) Best answer is to just forward them to cell phones or possibly the above mentioned $15 a month metered phone line for the alarm system. This means NO hardware needed to connect the analog phone system to the PBX, and CAN be an acceptable alternative to having two internet connections (for redundancy)
You can purchase flat rate unlimited incoming call business lines for as little as $8 a month, outgoing will run you about a penny a minute, maybe a penny and a half, for metered service of reasonable to excellent quality, up to about $20-40 a month for unlimited outgoing service.
More than two cents, I think I threw in a whole dollar!