If I may make a suggestion: If you're concerned about going dry loop, find out the install costs to go with the full price for the first month to get the service installed. You can always switch to the annual contract
afterward if you want to run with the lower price.
As for wiring, frequently, the phone company doesn't even disconnect the line going into the demarcation box after folks move out (let alone anywhere else, which would be on the telco end and none of your cost or concern). As long as the prior tenant didn't use FiOS and there's no corrosion on any of the connectors in the house (easy to check for and fix), you should be fine. Easiest way to check before even ordering is to
use a multimeter to check for voltage. If you're getting 48VDC across the green (+) and red (-) even without a dialtone, you know all the wiring is up and running already between your house and the
Central Office, and it's just a matter of "tossing a switch" to turn on the DSL service. (We dropped AT&T DSL for Cox cable two years ago, and we
still have phone voltage on the house jacks.)
Alternately, if you're
really worried, check into pricing on having Verizon install and fire up DSL service. Have them install and run that for a month or so, and then just switch over to DSLExtreme from there. (This might not be possible, I don't believe Verizon personally offers dry loop anymore... but it never hurts to check.)
Finally, I'd dealt with them on behalf of my grandmother for nearly three years in a Verizon area. She had decided to keep phone service, but had never had any sort of internet to her home before the DSLExtreme install than dial-up. With the exception of a bit of an issue between it and her
PERS system (I wasn't local, so I couldn't fix it even though I knew what the problem was - her internet connection would drop when the monitoring company would "check in" - the PERS box never got a proper DSL filter), it worked fine. IIRC, when it came time to pull service last year while she was in the middle of a contract, my aunt and uncle mentioned no difficulty terminating service with no penalties due to circumstances.
Just approach it smartly, do a bit of prep-work, and don't go under contract to save $10 a month until after you know it works.