Hey hun.
I can really only echo what the others have said.
personally i think you need to sit down with with, as sticky has suggested. the more you let it eat you up inside the worse it will get, and if this does turn out to be completly innocent, you will struggle to move on from it. If he is only 'chatting' then you need to be shown proof, that it isnt what you think, so that you can put your own mind to rest. Also, i do think its innapropriate for these woman to have his mobile number, and i think you should ask him, as his wife to make sure he no longer recieves text messages from them or sends any.
- my OH sometimes chats to woman i'v never met, that he met a long time ago, or went to school with years ago, or woman who work in the office at his company but rarley sees. Some of these woman i know he has asked out previous to our relationship, or they have approached him. he doesnt always tell me when he's exchanged some messages, and although i'd prefer he did always say, the fact is i don't always tell him when i speak to old boyfriends, or male friends from my past that i no longer see. I know that his messages are never suspicious, and if i mention that iv seen a message, or ask him who he's talking too.. he is always honest and more often than not shows me what he's written. I do trust him, as he does me.. but i know some of the girls that he has been involved with, and they arn't very nice people, and could go out of thier way to try and hurt us.. it's not my place to tell him not to speak to them, as he has done nothing wrong and its not a continuous thing. I am just wary, but, in this case, you obviously think these messages could be somthing to worry about, and it is your place, as his wife to say somthing.. and as your husband, he should be honest and give the situation the attention it needs, to talk it out and resolve this issue.
*hugs* xxxxxxxxxx