話す練習をします 話す練習します The second one sounds very colloquial to me. I'd like to recommend you to use the first one, especially, in writing and in the formal situation. スポつをします --> スポーツをします スポつします --> スポーツします The same happens to these sentences. The second one is very colloquial and I use the first one in writing and in the formal situation. 電話をします 電話します I think they are correct and we use them very often. As René-san already explained, the first one is like "to do the phone call" and the second one is "to call (on the phone)". Other examples with the literal translation: 私は英語を勉強しています。(I study / I'm studying English.) 私は英語の勉強をしています。(I do / I'm doing the study of English.) Since I'm not a professional teacher, please wait for other answers. I hope this was helpful.

that is a good question. I've encountered both forms. if it is a noun that is also a "suru" verb, you can, I guess, technically use with and without "wo", and probably it would even translate the same in English (though literally you would would be saying (i) I'm speaking on phone or (ii) I'm doing a phone speaking). and what makes this all even more confusing is that if it is a noun that is not a "suru" verb, then you should use "wo", but Japanese, especially in some regions, are very lax about the use of particles and often drop a lot of them, including the "wo".