I don't have AppWorld on my Storm so I needed an OTA link too. The YouMail site does not seem to advertise one but I found an article about YouMail from the beginning of the year that had an OTA link. It's for v.0.95.9 and is 306KB in size. I'm assuming this is a current version. I just downloaded and installed on my BB and it seems to be working fine. I'm uploading my contacts right now.
I currently have 0.96.1, my wife has the newer version but she's not home for me to get the number. I have contacted their tech support about this issue b/c I cannot d/l app through app world, but it is because I have a legacy Alltel number on a VZW device and plan. App World sees my number as still being a Alltel phone and blocks me from some apps (Not available for your device or for your carrier). Newer version that my wife has works much better than the one you get OTA from them, or the middle version I have.
This seems to be an old thread, but as good a place as any to put a link for the latest Blackberry YouMail app that I can find. This does not seem available anywhere else on the web; I pulled this COD from my old BB 9780 running OS6 and re-installed it on an OS7 device - with success! NOTE: This is not an OTA JAD file. I used BBSAK to install the COD, but it was quick and easy. Also NOTE, I have included a fix for Blackberry Google Maps as well, as these files are also not easy to come by. I hope some of the below links will survive.