Yes, of course, between Poland and the Czech Republic, regular buses run. EuroLines, Student Agency, Inter-Bus, Polski bus and some other companies are engaged in transportation of passengers there.

By direct bus to Prague, you can get from Warsaw (journey time 12-12.5 hours), Lodz (9.5 hours), Wroclaw (5 hours), Krakow (10 hours), Poznan (9 hours), etc. No transplant is required on a trip from Bialystok and Warsaw to Karlovy Vary, from Lodz to Pilsen, Hradec Králové, from the Polish capital to Brno, Pilsen, Mariánské Lázně (formerly Marenbad). There are direct and connecting flights between many other Czech and Polish cities.