I don't think it is weird if the mobile phone provider is allowing you to only sign up for messaging.
Although it could be a prepaid phone and then that may make a little more sense, if it is a contract plan and you have not signed up yet then you will probably be told that you need to choose an eligible voice plan.
Or in the case you have a SK you could chose the data only plan but that cost approx $44.99, the cell company would not be making a real profit if they let everyone just sign up for a text plan @ $4.99, but if you are already signed up then that is def a steal because many want you to have a voice plan and then you can add on Additional features like text messaging.
As far as weird, No I don't think it is. With the prices of plans today it makes sense to save where you can, if you are able to identify the fact that you rarely use the phone for talking then why waste that money.