It takes seconds to reply to a text, it's no effort at all.
Being ignored, especially by a 'friend' who normally replies is poor form.
I also hate the modern reliance on text and e-mail - dial the number and talk, it's easy.
Personally, no reply to the second text after a week when I know they have seen it means they get downgraded from 'friend' status to just 'someone I know'.
My genuine friends text, e-mail or call me back, because I'm important to them and vice versa.
If they're too busy, a quick 'hectic at the moment, call you at the weekend' or similar message is all it takes, if you care about someone and have any self awareness to appreciate that ignoring them could be misinterpreted or hurt their feelings.
I'll say it again, it takes seconds and is no effort.