enum.conf:

[general]
search => enum.kci.net



extensions.conf (pertinent sections):

[ob-local-tollfree]
; we can dial out the local trunk if it's toll free
exten => _18XXNXXXXXX,1,EnumLookup(${EXTEN})
exten => _18XXNXXXXXX,52,Dial(${TRK1}/${ENUM})
exten => _18XXNXXXXXX,53,Hangup

[ob-local-nxx]
; looks in nxx that are local to us, if matches dials out the trunk
; notice that we needn't strip the areacode, but do need strip the 1
exten => _NXXNXXXXXX,1,EnumLookup(${EXTEN})
exten => _NXXNXXXXXX,2,Dial(${ENUM})
exten => _NXXNXXXXXX,3,NoOp(${CALLERIDNUM})
exten => _NXXNXXXXXX,4,Hangup
exten => _NXXNXXXXXX,52,Dial(${TRK1}/${ENUM})
exten => _NXXNXXXXXX,53,NoOp(${CALLERIDNUM})
exten => _NXXNXXXXXX,54,Hangup
exten => _1NXXNXXXXXX,1,EnumLookup(${EXTEN:1})
exten => _1NXXNXXXXXX,2,Dial(${ENUM})
exten => _1NXXNXXXXXX,3,NoOp(${CALLERIDNUM})
exten => _1NXXNXXXXXX,4,Hangup
exten => _1NXXNXXXXXX,52,Dial(${TRK1}/${ENUM})
exten => _1NXXNXXXXXX,53,NoOp(${CALLERIDNUM})
exten => _1NXXNXXXXXX,54,Hangup



now some entries from the dns zone:

$ORIGIN enum.kci.net.

; if we get a 52124xx request, send to the pbx
; currently only short circuiting this in the context _from_ the pbx
*.4.2.1.2.5.0.7.9 IN NAPTR 100 10 "u" "E2U+sip" "!^(.*)(970)(52124..)(.*)$!\\3!" .
*.4.2.1.2.5 IN NAPTR 100 10 "u" "E2U+sip" "!^(.*)(52124..)(.*)$!\\2!" .

; outbound calls that are local should go out the trunk
;akron 345 554
*.5.4.3.0.7.9 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)(970)(.......)(.*)$!+\\3!" .
*.4.5.5.0.7.9 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)(970)(.......)(.*)$!+\\3!" .
;brush 842
*.2.4.8.0.7.9 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)(970)(.......)(.*)$!+\\3!" .
;crook 886
*.6.8.8.0.7.9 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)(970)(.......)(.*)$!+\\3!" .

;toll free 800 866 877 888
*.0.0.8.1 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)$!\\1!" .
*.6.6.8.1 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)$!\\1!" .
*.7.7.8.1 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)$!\\1!" .
*.8.8.8.1 IN NAPTR 100 10 "u" "E2U+TEL" "!^(.*)$!\\1!" .

; action
*.8.8.7.7.0.3 IN NAPTR 100 10 "u" "E2U+iax2" "!^(.*)(307)(.......)(.*)$!action/\\3!" .
*.0.2.2.8.0.3 IN NAPTR 100 10 "u" "E2U+iax2" "!^(.*)(308)(.......)(.*)$!action/\\3!" .
*.5.2.2.8.0.3 IN NAPTR 100 10 "u" "E2U+iax2" "!^(.*)(308)(.......)(.*)$!action/\\3!" .



the first section (52124XX) is our DID pool, so we keep them internally
second section is just a few of the entries that represent local NXX
third section is toll free stuff, we route out our trunk to save carrier fees
last section is a "sister" company that we peer with, so anybody local to them
  we deliver to their asterisk box