Sound propagation under ice in the Baltic is of interest for military as well as civilian purposes. Important questions are, for example, how sonar systems are affected by ice in shallow waters and how marine mammal life under ice is affected by ship traffic. Changing climate and increasing ship traffic are factors of great concern also in the Arctic region. Modeling results for sound propagation under ice in the Baltic Sea are presented, focusing on high frequencies. The sound propagation is influenced by bottom as well as ice-cap interaction in these shallow waters. The low-and high-frequency modeling is performed with wavenumber and ray models, respectively. Both types of models are amended to include a solid ice layer on top of the water column. In addition, the modeling efforts are extended to study the performance of an underwater communication system developed at FOI. Sea trials in the Gulf of Bothnia are planned, under ice-covered as well as ice-free conditions, to evaluate the modeling results.