If they do not respond to SMS messages for a long time, how to respond?
Either talk to her about this, find out what's what, or take this friend's habit for granted. In any case, there is too little information to give really good advice.
I faced a similar situation. Here, indeed, it is necessary to know the content of the SMS.
If your sms, for example, about how are you? Shall we go somewhere? remain indifferent to her almost always and for a long time - definitely, she doesn't care. She is in no hurry to meet with you and has no desire.
If she does answer, then she feels the obligation to answer, but most likely for the sake of decency.
If he answers positively, but always after a long time, he thinks for a long time what he will do and makes a decision.
If she is just always busy, and I need to ask something about further actions - and knowing about her such habit, I will call and ask online her plans.
If it's just a question that doesn't require some kind of confirmation, for example, What are you doing? How are you? She simply does not see the point in answering it, she is waiting for specific proposals for an exact answer.
In general, everything is individual. Knowing the specific situation and content, I can answer in more detail.
Everywhere and always you need to respond appropriately, including when you are not answered by SMS. There may be many reasons and explanations for this, a person may not see SMS, be busy, sleep, or have no funds on the balance sheet. But the most common reason, it seems to me, is the reluctance to respond specifically to your message.
What to do in such a situation? Talk to your friend, find out the reason for the silence in response to the SMS, if possible, eliminate this reason. And agree on another method of communication, for example, calls.
It depends on what kind of SMS (what content)? Maybe the content is inconvenient for not? She needs to think, or she is not inclined to talk about these topics. Perhaps she is forgetful, at first she thinks, I will answer later, and then forgets. Can she be very busy? Or doesn't like typing sms? If she is, as you write, your friend, then you can ask: why do you often delay with the answer? Knowing generally about this feature, you can take it into account in communication, call, for example, instead of SMS.
Try to call from another number, maybe the person just doesn't want to answer or you are on the black list.
SMS is a private form of email. It is instantly delivered, but the addressee is not obliged to read it instantly, let alone respond instantly. A mobile phone is a mobility option, but not a guarantee.
I am listing all these cellular basics just to remember:
No response is not a lack of desire to respond. The girlfriend can be in the bathroom, and the phone is in the bedroom. Or vice versa.
If you sent an SMS with the conditional "lightning" mark, then make a short call in a minute to draw attention to yourself and to your phone.
And nothing else needs to be done. This is both tactless and pointless.
Call or write endlessly until there is an answer.
Dear Ksenia, you yourself are wonderful knowing about a friend's habit, why "raise a noise"?
I myself, too, almost do not respond to SMS.
(it all depends on the degree of urgency)
That is, if someone wants to talk "live" ... I'm all in attention!
I can receive and respond to the "call back!" (After all, sometimes there is no money. Everything happens. And from my point of view, this is forgivable!)
and if the purpose of SMS is "secret negotiations" or "congratulations", then "zero" of my reactions (because a person who respects you will say DIRECTLY, not "hiding behind words").