Are you using the websites to send free texts? Also have you checked with the network to see what packages they have on your mobile? pay a little extra on T-Mobile and get cheaper texts to PL but it still costs me alot.
It's worth it though, mostly.
i use sheriffratings.com for free txts, you get ten to use per day but it actually works and it's completely free with no hidden charges to you or the person you're txting, but it works for uk mobiles only. not sure about international sms. can you send sms through skype?? i'm pretty sure it's possible to send sms through gadu-gadu you just gotta buy credit.