Don't want to drown you in links, but here are two more listing the advantages of those types of agreements (you can also say "agreements," as in BPAs):
https://www.gsa.gov/acquisition/purchasing-programs/gsa-sche...http://acqnotes.com/acqnote/careerfields/blanket-purchase-or...It's called "call-off" on other pages not because you call off or cancel the order, but because you call off or "release" supplies based on the agreement. You can also say "generate regular POs from the blanket one":
http://www.kb.blackbaud.co.uk/articles/Article/38363Maybe it's my migraine today, but I'm a bit confused about whether the entire agreement is the BPA and "Abrufstellung" means the releases against it here (so they don't make any promises regarding the frequency and value of releases) or whether they don't want to say how many BPOs they need.
Cf
"In dem zugrunde liegenden Vertrag sind oftmals Mindestmengen pro Abruf, die Häufigkeit der Abrufe...festgelegt..."
http://www.lagerwiki.de/index.php/AbrufbestellungIf "-stellung" in your question is not a typo for "-bestellung," the former would seem to be more likely than the latter.