Don't know what kind of financial situation you're in, but I used WIC last time around (and may have to again). They will give you food, juice, formula, baby cereal, etc., and you'll get some now since you have a little one and are pregnant. That might ease up some of the financial burden.
I just was thinking if I call the facility and give them the house number and tell them to let him know, if he calls me collect to call me on that number until I can get him a phone card... that's all. I am sure they won't be jerks about relaying the message over to him.
That sounds reasonable. But I wouldn't bend over backwards to get him the calling card and make yourself accessible while he's in rehab. Hopefully his attention will be focused on his recovery, and not on making sure you're waiting for him with bated breath. You know?