Bonding two T1s - Recommendations on solutions

What options are available to you?  Are both T1's from the same provider?  Routing protocol options depend on the provider/s.  This will deal with advertising your LAN to the upstream.
Do you have your own IPs?
You can setup the routing to load-balance the outgoing connections (caution needs to be taken to make sure a response to an incoming connection request leaves through the same T1).

What type of hardware are you running. It's somewhat hard to give a solution without knowing more in-depth about your setup. A particular solution available to Cisco hardware users is a feature called Optimized Edge Routing (OER). I am sure other vendors have similar features.

Actually this feature has been renamed to Performance Routing (PfR).

Try Googling these and seeing if this is a possibly solution for you.

if both are from the same ISP. your ISP need to set it up on their side too. in order to take the full 3Mbps up and down.
if it from different ISP then you do load balance, round robin, setup.  but you only have 1.5 Mbps speed to single connection.  

They currently have a Sonicwall tz170 as their primary router. This router has a T1 from one ISP and there is another T1 not doing anything at the moment. There is also a VPN to NY on this Sonicwall. I would like to be able to add the other T1 to a router or something without much disruption to the existing nework right away.