There are few mobile operators in Poland, but you got to watch a bit the prices and the bonuses you get. I went for Play Mobile (Polish only) for a 3G connection, and ERA (some English) for mobile phone (because my lovely girlfriend uses that).

Play has some decent pre-paid ‘na Kartę’ solutions and have good coverage (I think they use ERA?). You can buy a starter package for only 19 PLN (4.17 EUR) in lots of shops, for example in Kraków GSMCentral (maps). This ‘Starter’ gives you instant access and you pay 0.03 PLN (3gr or 0.006 EUR) for 100Kb traffic. Currently, there is a bonus of 1Gb on your first connect/reconnect. After this, you top it up for 50 PLN, for example, and get more than 4Gb, valid for 56 days.
The Play package comes with enough English instructions to get you going. The URLs, however, are all pointing to Polish websites and you’ll need a Polish bank account for recharge it online. No worries, there are enough shops where you can buy the so called ‘scratch cards’ which has a code you need to send via SMS.
For Mac OS X users: I’m using a USB Modem Huawei sold by Play which is apparently not locked. Software installs, and connects right away. You don’t really need the Play software, but it installs the modem driver. One problem with the Huawei stick is that it doesn’t fit nice in my MacBook Air’s USB.

It was quite a challenge to get information through Polish websites, and you got to be lucky bumping into people speaking English in shops, here in Kraków. However, Google Translate was a great help, as well as friends, colleagues, their contacts!

We work indeed from everywhere, ‘here’ at MySQL!