Hi, I'd like to help you with your question.
Even though you did find this information by snooping, you still can talk to him about it. This is devastating information to you and to have to keep it to yourself is too much. And if you try, it is going to hurt you and your marriage. The method of how you found out is not the issue here. Having an affair definitely is more damaging to your marriage than you looking at your husband's cell phone. If he had nothing to hide, then there would be no issue here.
Is there anyway to get more proof of his cheating? The reason you may want to try is because he might try to explain away his talking to this woman. If you have more proof, it is harder for him to try to explain his way out.
When you confront him, try to remain calm. The last thing you need is to have him yelling at you and becoming defensive. If you both are arguing, the problem will not get solved.
If he does confirm that he is cheating, it is important than you seek help right away, especially for you. You need support and someone to talk to about how you feel. Also, get the help of a therapist. You can find one by asking your doctor for a referral or if you attend church, your pastor can help. You can also search on line at http://therapists.psychologytoday.com/rms/.
You also have the right to ask him to not see this woman on his trip. You can even suggest he not go at all, if he would not lose his job over it. Your marriage is more important and if he does go, you cannot be sure he will not continue to cheat on you with her.
Insist that he cut this woman out of his life now and start working on your marriage. He needs to regain your trust and that takes work and determination. The therapist can help guide you. Here are some other resources to help:
Not "Just Friends": Rebuilding Trust and Recovering Your Sanity After Infidelity by Shirley P. Glass and Jean Coppock Staeheli
Infidelity: A Survival Guide by Don-David Lusterman
My Husband's Affair Became the Best Thing That Ever Happened to Me by Anne Bercht
You can find these books on Amazon.com or your local library may have them for you.
Let me know if I can help any further,