SIP trunk routing problem with same provider

Dear all,

I have two sip trunk with same provider.
I have two network interface card eth1 & eth2.
SIP trunk provider has given me two different ip for eth1 & eth2 & two different gateway.



Provider IP - (same for both sip trunk)

I have given static routing as below.

route add -host gw
route add -host gw

But only one register at a time because sip trunk takes only first route for both eth.

How can i make request to provider with different source ip on sip trunk?