The reactions to Rabbi Weiss allowing a woman to daven kabbalas Shabbos are perhaps typical of the jblogsphere. I saw someone write that he doesn’t know if it’s a halachic problem of kol isha or not, but it’s definitely not Orthodox (maybe more on that in another post), while others offered their own sevaros as to why kol isha is irrelevant without any regard to the sources. I don’t know where the discussion ends, but, like any other halachic issue, I don’t see how the discussion can even begin without looking at the sugya.
The Ba’al haIttur is quoted as saying that a women may not read megillah for men because of kol isha. Were that all there is to say, this would be a very short discussion. I don’t think there is much wiggle room to distinguish between reading megillah and davening kabbalas shabbos.
However, not only do the other major Rishonim not mention a concern of kol isha (in fact, according to Rashi women may read the megillah for men), but there also seems to be an open gemara that proves kol isha is not a problem in this context. Chazal tell us (Meg 23a) that a woman could theoretically get an aliya on Shabbos -- and in the days of Chazal the one who got an aliya would read the parsha – if not for concern for kavod hatzibur (which Rishonim define in different ways and is a separate discussion). If reading megillah or reading the Torah with the trop / tune constituted kol isha, why would the gemara invoke the principle of kavod tzibur and not the categorical issur of kol isha? With a little thought one can even come up with potential nafka minos where kavod hatzibur is not a problem (can a tzibur be mochel their kavod?) but the prohibition of kol isha would remain in force – so why not mention the more encompassing issur?
The reason to exclude Torah reading from the prohibition of kol isha is easy to understand if one assumes that the issur of kol isha is a safeguard to prevent a man from being tempted to immorality by the seductive voice of a woman. The singing of Torah pesukim in the context of davening is unlikely to be the sort of seductive singing that would lead to sin. Along these same lines, the Sdei Chemed quotes the Divrei Cheifetz that singing “zemiros kodesh” is not a problem of kol isha.
In a nutshell, that’s how the battle lines shape up (of course, with more detail and nuance found in the sources). On the one hand: the Ba’al haIttur. On the other hand, a sevara to the contrary rooted in logic advanced by earlier and bolstered by a question from an open gemara against the contrary position. Whether that's enough to convince you is the question.
Again, the same rules that apply to other issues apply here. The discussion starts with the sources, but discretion and good judgment are the final arbiters of what should be done in practice.