Create a multilink interface
interface multilink 1
ip address x.x.x.x y.y.y.y
ppp multilink
ppp multilink group 1
Assign the individual serial interfaces to the multilink group
Controller e1 1/0
channel-group 0 timeslots 1-31
controller e1 1/1
channel-group 0 timeslots 1-31
interface serial 1/0:0
no ip address
encap ppp
ppp multilink
ppp multilink group 1
interface serial 1/1:0
no ip address
encap ppp
ppp multilink
ppp multilink group 1
http://www.cisco.com/en/US/products/hw/routers/ps4062/products_configuration_guide_chapter09186a008076fdce.html#wp1055832
HTH, rate if it does
Narayan