It will most definitely not get ICS... they never even gave it Gingerbread. As for development with using custom ROMs....the CDMA versions (Verizon & Sprint) were left out of the loop. The T-Mobile & AT&T versions got all of the attention for hacking the devices.
Samsung has pretty much abandoned the 7" tab. It was their first tablet and have moved on to the Galaxy Tab 10", 8.9" and 7" plus which is an updated version of the original 7" tab.
The 7 plus runs on Honeycomb... which is the OS that was designed for tablets. I doubt the 7 plus will ever see ICS either. Most likely the 8.9 and 10" versions will eventually get it.
The original 7" runs on Froyo... which basically makes it feel like you're using a giant phone. It does work pretty decent though. I just upgraded from the 7" and now have the 8.9". I enjoyed it while I owned it. It gets the job done.
If you're looking for a 7" tab for around $150... you might want to check out the HTC Flyer. Its a better tablet and is going for about $200. Other then that... for $150 its not a bad deal for the Galaxy Tab if you really want it. There's also the Asus Transformer which is a great tablet but its 10" and goes for about $300 but that price will most likely drop a little when the newer Asus Transformer Prime is released....which should be sometime soon.
For making phone calls on the tablets.... you can use Google Voice.
https://www.google.com/voice
And I never tried it but I do believe a stylus works with the tab.