First off let me say I absolutely love my Obi100, it was a great purchase and ditching my landline is a great feeling! Thanks for making such a simple yet powerful product, I wish every hardware purchase I made was this good.
I, like many many other people purchased a 32gb HP Touchpad and would absolutely love a way to connect to my Obi100 with it. I have the application for my Android phone and on my daughters iPod touch and they work great, it would be fantastic to have the same functionality on my tablet.
From what I've read development for WebOS isn't very painful in comparison to other platforms. The best thing about developing for WebOS is that you can make one app (designed for WebOS phones) and it will be compatible on the tablets also. A tablet version could also be created but I personaly don't think that extra work is necessary, it would be fantastic but not entirely necessary.
There are a boatload of people with WebOS phones and tablets, many I'm sure have your product and would also like this functionality. The more platforms you support the more devices you'll sell. WebOS is not going anywhere anytime soon (HP has promised that and so has the open source community) and all those firesale devices (phones AND tablets) are flooding the market, it's a whole new wave of customers out there for you!
Please please please!