To make a voice call, you need to have a usable signal continuously for the time it takes to dial, get the other person to answer, say what you have to say, and possibly get a reply.

To send a text message, even if you have no signal at the moment, you can type the message and have it waiting in the "outbox". Then you can wander around waving the phone in the air or whatever. If the phone sees a usable signal, even for a moment, it can send the message.

Likewise, since text messages are short and can be queued up to send in the gaps between voice calls, they should be helpful for getting through during times of very high traffic.

Now, *in general* a low-bandwidth text message can be sent with a much weaker signal and more interference than a high-bandwidth voice transmission. I don't know to what degree actual cell phones take advantage of this fact.

Finally, be aware that I personally don't have a lot of experience in using cell phones with poor signals as I live in an area where the coverage is virtually continuous.