I know I'm late to reply here, but Knitterly, I think your friends are being inconsiderate. Im finding it hard to beleive that adults can't remember who texts and who doesn't. I have some friends who are constantly available, and some, like my sister in law, who just dont text. She has a full plan, and just got a smart phone, but rarely texts. If I text her, I know she might not get it for a few days, so if there is anything timely - I call her. My dad can text and email - but he responds faster to email. so I email. My grandmother just learned to text, so now i text her, but expect her to take days to respond - its still faster than email for her, and as she is in Florida for the winter - and I'm in Canada, text is the easiest way to reach her.
Knitterly, I think Id just remind friends that you dont check your phone often, just as you have done. I think its great that you are being more proactive to check your phone more often. I wish you luck with your friends.