I'm not sure how other plans work, but my SERO plan covers unlimited roaming which includes 1X data and texts, so it's not really a problem for me. When I roam on verizon and text myself, I get my text back within seconds, it's quite amazing
After some experimentation, my texting lag is still about the same, hasn't gotten better or worse. Most of my texts come in a timely fashion, but I sent out a picmail a few days ago that was received 4 hours after I sent it..