SMS App

Help! Please, you lovely clever peoples! I have a mate who lives in Holland and we would love to keep in touch with each other via text message, however, there is a snag. For her to send me a message, I live inthe UK, it costs her money and to chat this way for any length of time would add a small fortune to her phone bill. I am only on a payg mobile so when I tried to reply to her sms, I couldn't. I think it is because I am only on payg and not contract.

She mentioned something about an app that lets you send and receive regular text messages via the internet/wifi rather than just send it like a regular text message to someone else in the UK over your network provider. Does such a thing exist? I have had a look out there and the only things I found were apps that let you clump all your contacts together, similar ones to Timescape, that's not what I am looking for.

I hope someone can help me. I have a Sony Ericsson Xperia X8 if that helps.

Thank you.