There's little you can do with your money on the prepaid sim card in the Play besides some calling and texting - certainly you can't move it to a different account/prepaid card - I doubt such possibility exist currently in any Poland's network on prepaid.
It's worth to add, that if you want to 'withdraw' some of the phone money into your bank account in Poland you can check some online services which offer such possibility. Remember however, that the regular money 'recovery' rate is about 30% - I found one site though, where they claim that you'll get back 50% and more of the money you sent them via a premium sms (it works that way in another places too) - see this:
Some networks (not Play in pre-paid) allow to transfer money from one account to another in the same network. But between the networks - not. It's also not possible to exchange it back to real money, except for the mentioned services, where you lose a lot.
Translating: - send SMS to the number 5511 with the content: P [amount of money to transfer] [target phone number], wait for an incoming SMS with confirmation, send a confirming SMS with the content:
- costs 0,05 PLN - the time of validity of the account to which you send the money is not lengthened - within 30 days you can send or get maximum 30 PLN - users of the offers Sami Swoi and 36,6 cannot use this (BTW, AFAIK, the first one doesn't exist any more)
In Orange it was possible to 4 March 2013.
Each of the 4 main networks allows to send money to a pre-paid user by a regular subscriber (paying bills on the post-paid rules).
Thanks kpc. I once heard about such service in Plus but I thought they abandoned this already. But the amount of 20PLN (not 30 as I see?) total per month is weak.. Better than nothing though - it should be available in every Polish network.