Data Plan Ran Out - Error Messages

[bxhxdlsb]

I have a 20mb plan, and my month of prepaid is about up. When trying to download a picture message or connecting to GPS service, it will not connect. How can i utilize a wifi connection to do these things? Even when i have my data plan back, i'd like to use wifi for things like these. and only use data plan memory when away from wifi hotspots.