Note that summon holy symbol even explicitly states that it has no value.

Does being without value exempt it, though? Does the list include "and any number of valueless things"?

@BenBarden it's a valueless spell focus at that point. You can put it in your (explicitly allowed) spell component pouch.

"A spellcaster with a spell component pouch is assumed to have all the material components and focuses needed for spellcasting, except for those components that have a specific cost, divine focuses, and focuses that wouldn’t fit in a pouch." It's not included as part of the pouch (divine focus), and the fact that you can fit it into the pouch doesn't change the rules for Vow of Poverty.

If we're going extreme RAW here, the only argument I can see that might save it would be to claim that, as a spell effect, it doesn't count as a "material possession". Other than that, you are using it, and it's not on the list of specific exceptions.

@BenBarden The way I have usually seen that argued is that it doesn’t count as a “material possession” since it is temporary and worthless. I’ll admit I had thought the Vow was more explicit about that, though; that appears to be a consensus that I’ve internalized.

It's like you said. "If you have to ask...." The absurd strictness rabbit hole. It goes deep.

@BenBarden Oh, I completely agree. The entire premise of the question is based on the absurd strictness of not allowing a 1-gp wooden holy symbol to a cleric in the first place, which I think is idiocy but then my gripes with this feat (this book) don’t stop there so whatever. If that’s what we’re working with, I feel like we can’t cut any corners—cuz if we did, we’d just allow the holy symbol in the first place. Hence, I’ve added a caveat to my answer.

Strictly speaking, VoP forbids owning or using material possessions, even temporarily, and even if they're valueless. You can't use a real physical holy symbol even if it was conjured.

@QuadraticWizard Strictly speaking, that’s not clearly the case, unless you know of a strict definition of “material possession” that I am unaware of.

According to an obscure rule under the Summoning subschool, "a summoned object is not sent back unless the spell description specifically indicates this." The spell would permanently summon a real, non-magical, wooden holy symbol, which a VoP cleric may neither own, nor use.

@BenBarden good point. I forgot it excluded divine focuses.

@QuadraticWizard The duration on summon holy symbol constitutes specifically indicating that the holy symbol goes away, in my opinion. Else, what would the duration even do? (You can argue that it doesn’t and the duration is pointless, I suppose; RAW doesn’t have to be sensible. But there isn’t enough to say it can’t be the other way. The rules as written are ambiguous here.) Anyway, it’s clear you don’t buy the argumentation that it doesn’t count as a material possession; that’s fine. It’s not as explicit as I’d like. I still think it’s worth mentioning, plus Worldly Focus is an answer.

The full line (omitted for brevity in my previous comment) is "When the spell ends or is dispelled, a summoned creature is instantly sent back to where it came from, but a summoned object is not sent back unless the spell description specifically indicates this." This more clearly defines that a summoned item is permanent even if the duration runs out (perhaps not the intent of the spell's author, but we're playing the rules-as-written game for the purposes of this question.)

@QuadraticWizard Yeah, that line is ridiculously confusing. It makes no sense for even core Conjuration (Summoning) spells like secret chest or summon instrument. Really the only spell it makes any sense for is instant summons, which means it should be part of that spell and not the general Conjuration (Summoning) section. But true enough, that’s where it is, so I guess that’s what we have to go on. (Also, for the record, I’ve checked and Rules Compendium repeats the core rules on this subject.)

@QuadraticWizard Anyway, updated answer to remove summon holy symbol as an option, and noted why.