Probably not what you want to hear, but I think it's overwhelmingly likely that this is his phone and that he's been having an affair.
The reaction just doesn't add up any other way.
I think you know it deep down too.
You could retrieve the sim info, but it isn't going to change his story - unless content of texts might prove it has to be him.
The most effective way to sort this out would be to tell him that evidence shows you that he is having an affair, and to ask him to leave.
This doesn't mean that you split. The board is full of women who have muddled through at this stage, too scared to take a hard line. Life then becomes a mess of paranoia and uncertainty, and the relationship disappears in a sea of bitterness and distrust. It's only when there's an explosion- either proof appears OR the wife cracks and throws him out- that things can start to get worked out.
You know your husband is a liar who will try and bluster, bully and accuse others of lying to cover his tracks. Whether he's having an affair or not, that behaviour is going to kill your marriage, sooner or later.
Tell him you're as certain as you can be that he's having an affair. You're 100% certain that he's a liar (the smoking) so affair or not, you can't believe a word he says anyway. And you don't want to be in a relationship with a potential cheat who has so little respect for you and the family that lying is a way of life.
Tell him to leave, think about what he wants and to come back when he is ready to be honest about what's been happening in his life for the last few weeks/months. Tell him there us NO POINT in lying, if he lies now, WHEN you find out the truth, it will be divorce, no discussion, no second chances.
Harsh in the extreme and horrendously difficult to do especially with a baby. But I tell you, probably the ONLY way you will raise the ante here enough to shake this idiot into realising that he can't treat you like a dumb fool. Because that is what he is doing at the moment, and he thinks that that's all he has to do to get you to shut up and leave it.