He advantages of multilik are that you can bond multiple T1's to act as on cirucit.
Here is a configuration example.
interface Multilink1
ip address 192.168.1.X 255.255.255.252
ppp multilink
ppp multilink links maximum 2
ppp multilink links minimum 1
ppp multilink group 1
!
interface Serial0/0
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 1
!
interface Serial0/1
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 1
!