I have sprint coverage why does boost say no?

I have a Sprint postpaid account.

Looking to see about going to Boost instead because I want the multi line pricing boost has going on.

Boost shows voice coverage but no data at my home, but sprint gives me both. Likewise Virgin Mobile's coverage map shows I have voice and data where I live. Sprint coverage shows voice and data - and I get voice and data on Sprint. Using it now!

I'm on a kickstarter plan and need a second line. Due to my credit they won't let me have one unless I go into a store, which makes me nervous... chronic health issues recovering credit. Boost being prepaid wondering if its more my style anyway, as on sprint i've been paying them for a few months in advance anyway when i go to bill pay.