weird connectivity issue between serial0 connection and a switch

I have a Cisco 1720 router with a T1 CSU/DSU WIC in it.  The building has a T3 that it splits up and gives to the companies in the building.  They have given us an IP address that I used for the serial interface.  After I configured the router (config to follow...), the WIC was in alarm.  Couldn't figure out why.  Eventually, I transformed an RJ-45 Ethernet cable into an RJ-48C cable (spliced wires 1,4 and 2,5) and the amber alarm light went off.  Serial0 interface now shows as UP.  However, the lights on the Router are all green, but there is no light on the switch.  It's like the switch doesn't see it.  I've switched cables, ports, etc. to no avail.  The local network behind the router cannot access anything outside the router.  Any ideas what is wrong?  Here's the router config:

version 12.1
no service single-slot-reload-enable
service timestamps debug datetime localtime
service timestamps log datetime localtime
service password-encryption
!
hostname router_axx
!
no logging buffered
no logging buffered
logging rate-limit console 10 except errors
enable secret 5 $1$DNwM$rmHCiTTpun2RRBHm4kK6f.
!
memory-size iomem 25
clock timezone MST -7
clock summer-time MDT recurring
ip subnet-zero
no ip finger
ip name-server 12.127.xxx.71
ip dhcp excluded-address 10.20.20.1
ip dhcp excluded-address 10.20.20.251
ip dhcp excluded-address 10.20.20.252
ip dhcp excluded-address 10.20.20.253
!
ip dhcp pool ais
   network 10.20.20.0 255.255.255.0
   default-router 10.20.20.1
   domain-name ais_regus
   dns-server 12.127.xxx.71
!
!
!
!
interface FastEthernet0
 ip address 10.20.20.1 255.255.255.0
 ip access-group 100 in
 ip access-group 100 out
 ip nat inside
 speed auto
 full-duplex
 no cdp enable
!
interface Serial0
 ip address 12.41.xxx.30 255.255.255.224
 ip nat outside
 no cdp enable
!
ip nat pool nat-pool 12.41.xxx.30 12.41.xxx.30 netmask 255.255.255.240
ip nat inside source list 1 pool nat-pool overload
ip classless
ip route 0.0.0.0 0.0.0.0 Serial0
no ip http server
!
access-list 1 permit 10.20.20.0 0.0.0.255
access-list 100 permit tcp any any
access-list 100 permit udp any any
access-list 100 permit ip any any
access-list 100 permit icmp any any
no cdp run
!
line con 0
 transport input none
line aux 0
line vty 0 4
 password 7 14300705020D397B2A
login
!
no scheduler allocate
end