Several offers would meet your needs. If you want a lot more data than that, T-Mobile has a card for 5 zloty (=1.20 EUR) with 1 GB to start off, and 30 zl for 6 GB. I THINK they allow VOIP, but don't quote me. (Sorry, bit of a hurry here.)
http://www.t-mobile.pl/pl/oferta_spe...ernet-na-karte
Then there's Heyah, which has cheap international calls and an English site plus 100 MB internet per day (but no longer has decent validity - not a big deal for a short visit):
http://www.heyah.pl/english
Lycamobile has cheap calls, cheap Internet, and a sort-of English website. SIMs slightly harder to find, though:
http://www.lycamobile.pl/po/
And Play, Plus, and Orange probably also have deals that would do what you want. Reception is pretty much the same on all networks. SIMs are dirt cheap, so you can always change your mind or get more than one.