If you are just sending text (temps, precip etc), and it is encoded in utf-8, a character is a byte, so 250mb is 250,000,000 characters (could be slightly more if your carrier considers an mb to be 1024 kb instead of 1000). With 720 hours in a month, each weather report would have to be >347222 characters to run over the limit and you should be fine by a pretty wide margin.