I dont know what the halacha is. I try to follow the guidelines as set down by the shul I am davening in. In my neighborhood there is a shul that has a posted policy that asks all collectors to refrain from collecting from yishtabach until after shmone esrei. Another that has a posted notice asking all to refrain from collecting in the shul the entire davening and others with no request at all. I assume, rightly or wrongly that the Rav of the shul has done his homework before posting the request.
I remember an incident that occurred in the shul that instituted the "no collecting during davening", shortly after the policy went into effect. Someone related the following story to the Rav of the shul. 250 years ago, the leaders of the city of Vilna (parnassei hair?) wanted to enact a takanah that nobody be allowed to collect tzedaka in the streets, and instead should go to the gabbai. They felt that it would improve the decorum in the streets. They wanted the Haskamah of the Gra before enacting this takanah. He replied, why come to me, this was already approved by the Vaad Arbah Aratzos. They came back later and said to the Gra, we checked through the seforim of the Vaad and we can not find such a takanah. He replied, you misunderstoood, the Arbah Aratzos I was talking about are Sedom etc.. (yes, some were taken aback at the brashness of this fellow and the implicaiton of the story). The Rav told him, i am aware of the story, and your analogy of the shul policy to that story is flawed. I am wiling to discuss it with you in my office after davening. What happened during the discussion, I dont know, but the policy is still in effect.